Aerial vehicle with different propeller blade configurations

ABSTRACT

Sounds are generated by an aerial vehicle during operation. For example, the motors and propellers of an aerial vehicle generate sounds during operation. Disclosed are systems, methods, and apparatus for actively adjusting the position and/or configuration of one or more propeller blades of a propulsion mechanism to generate different sounds and/or lifting forces from the propulsion mechanism.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation-In-Part of U.S. patent applicationSer. No. 15/078,899, filed Mar. 23, 2016, entitled “Coaxially AlignedPropellers Of An Aerial Vehicle,” which is incorporated herein byreference in its entirety.

BACKGROUND

Sound is kinetic energy released by the vibration of molecules in amedium, such as air. In industrial applications, sound may be generatedin any number of ways or in response to any number of events. Forexample, sound may be generated in response to vibrations resulting fromimpacts or frictional contact between two or more bodies. Sound may alsobe generated in response to vibrations resulting from the rotation ofone or more bodies, such as propellers. Sound may be further generatedin response to vibrations caused by fluid flow over one or more bodies.In essence, any movement of molecules, or contact between molecules,that causes a vibration may result in the emission of sound at apressure level or intensity, and at one or more frequencies.

The use of unmanned aerial vehicles such as airplanes or helicoptershaving one or more propellers is increasingly common. Such vehicles mayinclude fixed-wing aircraft, or rotary wing aircraft such asquad-copters (e.g., a helicopter having four rotatable propellers),octo-copters (e.g., a helicopter having eight rotatable propellers) orother vertical take-off and landing (or VTOL) aircraft having one ormore propellers. Typically, each of the propellers is powered by one ormore rotating motors or other prime movers.

With their ever-expanding prevalence and use in a growing number ofapplications, unmanned aerial vehicles frequently operate within avicinity of humans or other animals. When an unmanned aerial vehicle iswithin a hearing distance, or earshot, of a human or other animal,sounds generated by the unmanned aerial vehicle during operation may bedetected by the human or the other animal. Such sounds may include, butare not limited to, sounds generated by rotating propellers, operatingmotors or vibrating frames or structures of the unmanned aerial vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of an aerial vehicle, according to an implementation.

FIG. 2 is a view of a propulsion mechanism with telescoping propellerblades, according to an implementation.

FIG. 3 is another view of a propulsion mechanism with telescopingpropeller blades, according to an implementation.

FIG. 4 is another view of a propulsion mechanism with telescopingpropeller blades, according to an implementation.

FIG. 5 is another view of a propulsion mechanism with telescopingpropeller blades, according to an implementation.

FIG. 6 is a view of a propulsion mechanism with different dimensionpropeller blades, according to an implementation.

FIG. 7 is a top-down and side-view of a propeller blade with propellerblade treatments, according to an implementation.

FIG. 8 is a top-down and side-view of a propeller blade with propellerblade treatments, according to an implementation.

FIGS. 9A-9C illustrate views of an adjustable propeller blade, accordingto an implementation.

FIG. 10 illustrates a view of another adjustable propeller blade,according to an implementation.

FIG. 11 illustrates a view of an adjustable propeller, according to animplementation.

FIGS. 12A-12B illustrate additional views of an adjustable propeller,according to an implementation.

FIG. 13 depicts a view of another aerial vehicle, according to animplementation.

FIG. 14 depicts an illustration of induced flows from coaxially alignedpropellers, according to an implementation.

FIGS. 15A-15B depict a motor with a pair of coaxially alignedpropellers, according to an implementation.

FIG. 16 illustrates a view of coaxially aligned propellers, according toan implementation.

FIG. 17 is a flow diagram illustrating an example propeller adjustmentprocess, according to an implementation.

FIG. 18 is a flow diagram of an example propeller adjustment process,according to an implementation.

FIG. 19 is a view of another view of an aerial vehicle, according to animplementation.

FIG. 20 is a block diagram of one system for active propeller adjustmentand sound control, according to an implementation.

DETAILED DESCRIPTION

The present disclosure is directed to controlling, reducing, and/oraltering sound generated by an aerial vehicle, such as an unmannedaerial vehicle (“UAV”), while the aerial vehicle is airborne. In someimplementations, one or more of the propeller blades of a propeller maybe adjustable, laterally and/or rotationally. For example, the propellerblades may be extendable away from a motor that is used to rotate thepropeller blades and/or be retractable toward the motor. In such aconfiguration, the lifting or thrusting force generated by thepropellers may be altered by adjusting the position of one or more ofthe propeller blades, without altering the revolutions per minute(“RPM”) of the motor. Likewise, the sound generated by the rotation ofthe propeller will also be altered due to the different position of thepropeller blades.

In other implementations, the size, shape, camber, chord length, line,thickness, pitch, etc., of one or more propeller blades of a propellermay be altered during flight. Such alterations will alter the lifting orthrusting force generated by the propeller blade and also alter theproduced sound profile of the propeller blade.

In some implementations, propellers of the aerial vehicle are alignedcoaxially along a motor shaft. The propeller blades may be configured torotate in the same direction (co-rotation), are in rotational phasealignment, and may be separated a defined distance so that the highpressure pulse of the induced flow from the lower propeller is canceledout by the high pressure pulse of the induced flow from the upperpropeller. In other implementations, the coaxially aligned propellersmay have different lifting and/or sound producing properties. Forexample, one of the propellers may have larger propeller blades thatgenerate a first lifting force and a first sound profile when rotated bythe motor at a defined RPM. A second propeller of the coaxially alignedpropellers may have a different configuration (e.g., different diameter,different chord length, different camber, different pitch, etc.) andgenerate a second lifting force and a second sound profile when rotatedby the motor at the defined RPM. In such a configuration, the differentpropellers may be individually engaged by a propeller adjustmentcontroller so that the different lifting force or different soundprofile may be utilized at different segments of a flight of the aerialvehicle. The non-engaged propeller(s) may either be allowed to rotatefreely or may be locked into a fixed position.

In other implementations, the distance between the propellers, alignmentof the propellers, and/or propeller blade configurations (e.g., camber,pitch, cord length, diameter, etc.) may be altered to reduce the soundgenerated by the induced flow from the rotation of the propellers. Forexample, as the coaxially aligned propellers rotate, the sound generatedby the high pressure pulse from the induced flows may be measured andone or more of the alignment of the propellers, the distance between thepropellers, and/or one or more propeller blade configurations of one ormore of the propeller blades may be altered to alter the sound generatedby the rotation of the propellers.

In some implementations, not all of the propulsion mechanisms mayinclude coaxially aligned and stacked propellers. Likewise, in someimplementations, the distance between coaxially aligned and stackedpropellers may be fixed, rather than adjustable. In such aconfiguration, the aerial vehicle may include two or more coaxiallyaligned and stacked propellers that will function primarily as a liftingpropulsion mechanism and be configured to generate a force sufficient tolift the aerial vehicle and any engaged payload. In addition, the aerialvehicle may include one or more maneuverability propulsion mechanisms,such as propeller and motor pairs, that may be used to maneuver theaerial vehicle during flight. The lifting propulsion mechanism(s) and/orthe maneuverability propulsion mechanism(s) may include coaxiallyaligned and stacked propellers, single propellers, or other forms ofpropulsion. Likewise, one or more propeller configurations and/or theposition of the propeller blades may be adjustable, as discussed herein.

In some implementations, the coaxially aligned and stacked propellersmay be adjustable. For example, it may be determined whether soundreduction is necessary. If sound reduction is not necessary, theposition of the propellers may be adjusted so that they areapproximately ninety degrees out of rotational phase alignment to oneanother. While such a position may result in more sound, the liftgenerated by the pair of propellers and/or the efficiency of thepropulsion mechanism may be increased. However, if it is determined thatsound reduction is desirable, the position of the propellers may beadjusted so that the propellers are phase aligned and the high pressureforces at least partially cancel out, thereby reducing the soundgenerated by the rotation of the propellers. Alternatively, one or moreof the coaxially aligned and stacked propellers may be disengaged sothat it is not rotating and generating additional sound. As anotheralternative, the position of one or more of the propeller blades may bealtered so that the sound and/or lift generated by the propeller bladeduring rotation is modified.

In some implementations, one or more sensors may be positioned on theaerial vehicle that measure sound generated by or around the aerialvehicle. Based on the measured sound, the position of the one or more ofthe propeller blades and/or one or more propeller blade configurationsmay be altered to generate an anti-sound that, when combined with thesound generated by the aerial vehicle, alters the sound generated by theaerial vehicle. For example, a processor of the aerial vehicle maymaintain information relating to the different sounds generated bydifferent propeller blade positions and/or configurations. Based on themeasured sound and the desired lifting force to be produced by thepropeller, propeller blade positions and/or propeller bladeconfigurations are selected that will result in the propeller generatingan anti-sound as it rotates that will cause interference that cancelsout, reduces, and/or otherwise alters the measured sound when thepropeller is rotating at the desired rotational speed. Such interferencemay be a destructive interference or a constructive interference.

In some implementations, measured sounds may be recorded along withand/or independently of other operational and/or environmental data.Such information or data may include, but is not limited to, extrinsicinformation or data, e.g., information or data not directly relating tothe aerial vehicle, or intrinsic information or data, e.g., informationor data relating to the aerial vehicle itself. For example, extrinsicinformation or data may include, but is not limited to, environmentalconditions (e.g., temperature, pressure, humidity, wind speed, and winddirection), times of day or days of a week, month or year when an aerialvehicle is operating, measures of cloud coverage, sunshine, surfaceconditions or textures (e.g., whether surfaces are wet, dry, coveredwith sand or snow or have any other texture) within a given environment,a phase of the moon, ocean tides, the direction of the earth's magneticfield, a pollution level in the air, a particulates count, or any otherfactors within the given environment. Intrinsic information or data mayinclude, but is not limited to, operational characteristics (e.g.,dynamic attributes such as altitudes, courses, speeds, rates of climb ordescent, turn rates, or accelerations; or physical attributes such asdimensions of structures or frames, numbers of propellers or motors,operating speeds of such motors) or tracked positions (e.g., latitudesand/or longitudes) of the aerial vehicles. In accordance with thepresent disclosure, the amount, the type and the variety of informationor data that may be captured and collected regarding the physical oroperational environments in which aerial vehicles are operating andcorrelated with information or data regarding measured sounds istheoretically unbounded.

The extrinsic information or data and/or the intrinsic information ordata captured by aerial vehicles during flight may be used to train amachine learning system to associate an aerial vehicle's operations orlocations, or conditions in such locations, with sounds generated by theaerial vehicle. The trained machine learning system, or a sound modeldeveloped using such a trained machine learning system, may then be usedto predict sounds that may be expected when an aerial vehicle operatesin a predetermined location, or subject to a predetermined set ofconditions, at given velocities or positions, or in accordance with anyother characteristics. Once such sounds are predicted, propeller bladepositions and/or propeller blade configurations that will result in thepropellers generating anti-sounds are determined. An anti-sound, as usedherein, refers to sounds having amplitudes and frequencies that areapproximately but not exclusively opposite and/or approximately but notexclusively out-of-phase with the predicted or measured sounds (e.g.,having polarities that are reversed with respect to polarities of thepredicted sounds). During airborne operation of the aerial vehicle, thepropeller blade positions and/or propeller blade configurations arealtered so that the propellers will generate the anti-sound. When theanti-sounds are generated by the propeller blades, such anti-soundseffectively interfere with some or all of the predicted sounds at thoselocations. In this regard, the systems and methods described herein maybe utilized to effectively control, reduce, and/or otherwise alter thesounds generated by aerial vehicles during flight.

In a similar manner, sound profiles for different propeller bladepositions and/or different propeller blade configurations at differentRPMs may be measured and a sound profile generated for differentpropeller blades. Likewise, an efficiency profile and/or maneuverabilityprofile may be determined for different propellers based on thepropeller blade positions and/or propeller blade configurations at thedifferent RPMS. During operation of the aerial vehicle, differentpropeller blade positions and/or different propeller bladeconfigurations may be determined and selected based on the desiredoperational profile of the aerial vehicle. For example, if the aerialvehicle is traveling at a high altitude between two locations, theoperational profile of the aerial vehicle during that portion of theflight may be to optimize for efficiency, rather than sound ormaneuverability. In such a configuration, propeller blades may bepositioned and/or have propeller blade configurations adjusted so thatthe motors rotating those propeller blades are operating in their mostefficient range, thereby reducing the amount of power required toaerially navigate the aerial vehicle.

In comparison, if the aerial vehicle is descending toward a deliverydestination, the operational profile of the aerial vehicle during thatportion of the flight may be to optimize for sound reduction and/oragility, rather than efficiency. In such a configuration, propellerblades may be positioned and/or have propeller blade configurationsadjusted so that the sound produced by the rotation of the propellerblades is reduced or otherwise altered and/or so that the aerial vehicleis more agile and maneuverable. In such a configuration, the powerconsumed by the rotation of the motors may be increased.

While the examples discussed herein primarily focus on UAVs in the formof an aerial vehicle utilizing multiple propellers to achieve flight(e.g., a quad-copter, octo-copter), it will be appreciated that theimplementations discussed herein may be used with other forms and/orconfigurations of aerial vehicles.

As used herein, a “materials handling facility” may include, but is notlimited to, warehouses, distribution centers, cross-docking facilities,order fulfillment facilities, packaging facilities, shipping facilities,rental facilities, libraries, retail stores, wholesale stores, museums,or other facilities or combinations of facilities for performing one ormore functions of materials (inventory) handling. A “delivery location,”as used herein, refers to any location at which one or more inventoryitems (also referred to herein as a payload) may be delivered. Forexample, the delivery location may be a person's residence, a place ofbusiness, a location within a materials handling facility (e.g., packingstation, inventory storage), or any location where a user or inventoryis located, etc. Inventory or items may be any physical goods that canbe transported using an aerial vehicle.

FIG. 1 is a view of a vertical takeoff and landing (VTOL) aerial vehicle101, such as an unmanned aerial vehicle, according to an implementation.The aerial vehicle 101 includes four propulsion mechanisms 102-1, 102-2,102-3, and 102-4 spaced about a body 104 of the aerial vehicle 101. Inthis example, the maneuverability propulsion mechanisms include a motorand one or more propellers. As discussed further below, one or more ofthe propulsion mechanisms may include multiple coaxially aligned andstacked propellers, and/or propeller blades of one or more propulsionmechanisms may be adjustable with respect to the motor, and/or theconfiguration of one or more of the propeller blades may be adjustable.An aerial vehicle control system, discussed below with respect to FIG.20, which may be positioned within the body 104, is utilized forcontrolling the propeller motors for flying the aerial vehicle 101, aswell as controlling other operations of the aerial vehicle 101. Each ofthe propeller motors may be rotated at different speeds, therebygenerating different lifting forces by the different propulsionmechanisms.

The motors may be of any type and of a size sufficient to rotate thepropellers 102 at speeds sufficient to generate enough lift to aeriallypropel the aerial vehicle 101 and any items engaged by the aerialvehicle 101 so that the aerial vehicle 101 can navigate through the air,for example, to deliver an item to a location. The outer body or surfacearea of each propeller 102 may be made of one or more suitablematerials, such as graphite, carbon fiber, etc. While the example ofFIG. 1 includes four propulsion mechanisms, in other implementations,more or fewer propulsion mechanisms may be utilized. Likewise, in someimplementations, the propulsion mechanisms may be positioned atdifferent locations and/or orientations on the aerial vehicle 101.Alternative methods of propulsion may also be utilized in addition tothe propellers and propeller motors. For example, engines, fans, jets,turbojets, turbo fans, jet engines, and the like may be used incombination with the propellers and propeller motors to propel theaerial vehicle.

The body 104 or frame of the aerial vehicle 101 may be of any suitablematerial, such as graphite, carbon fiber, and/or aluminum. In thisexample, the body 104 of the aerial vehicle 101 includes four motor arms108-1, 108-2, 108-3, and 108-4 that are coupled to and extend from thebody 104 of the aerial vehicle 101. The propulsion mechanisms 102 arepositioned at the ends of each motor arm 108. In some implementations,all of the motor arms 108 may be of approximately the same length while,in other implementations, some or all of the motor arms may be ofdifferent lengths. Likewise, the spacing between the two sets of motorarms may be approximately the same or different.

In some implementations, one or more sensors 106 configured to measuresound at the aerial vehicle are included on the aerial vehicle 101. Thesensors 106 may be at any location on the aerial vehicle 101. Forexample, a sensor 106 may be positioned on each motor arm 108 andadjacent to the propulsion mechanism 102 so that different sensors canmeasure different sounds generated at or near the different propulsionmechanisms 102. In another example, one or more sensors may bepositioned on the body 104 of the aerial vehicle 101. The sensors 106may be any type of sensors capable of measuring sound and/or soundwaves. For example, the sensor may be a microphone, transducer,piezoelectric sensor, an electromagnetic pickup, an accelerometer, anelectro-optical sensor, an inertial sensor, etc.

In some implementations, some or all of the propulsion mechanisms mayinclude propeller adjustment controllers. Likewise, some or all of thepropeller adjustment controllers may be affixed to the propulsionmechanisms. Alternatively, some or all of the propeller adjustmentcontrollers may be moveable or otherwise adjusted during operation ofthe aerial vehicle and rotation of the propeller blade.

In some implementations, by measuring sounds at or near each propulsionmechanism 102 and altering the position, rotation, and/or configurationof one or more propeller blades of the propulsion mechanism 102 to alterthe generated sound, the measured sounds and anti-sounds at eachpropulsion mechanism are independent. Accordingly, each sensor andpropulsion mechanism may operate independent of other sensors andpropulsion mechanisms on the aerial vehicle and each may include its ownprocessing and/or memory for operation. For example, the processor mayreceive a commanded lifting force and determine propeller bladepositions, propeller blade configurations and motor RPMs that willproduce the lifting force and a desired sound profile. Alternatively,one or more sensors 106 positioned on the body 104 of the aerial vehiclemay measure generated sounds and a propeller adjustment controller maysend instructions to different propulsion mechanisms to cause thepositions and/or configurations of different propeller blades to bealtered, thereby generating different lifting forces and/or sounds.

Likewise, the aerial vehicle 101 includes one or more power modules 112.The power module 112 for the aerial vehicle may be in the form ofbattery power, solar power, gas power, super capacitor, fuel cell,alternative power generation source, or a combination thereof The powermodule(s) 112 are coupled to and provide power for the aerial vehiclecontrol system, the propulsion mechanisms, and the payload engagementmechanism. In some implementations, one or more of the power modules maybe configured such that it can be autonomously removed and/or replacedwith another power module. For example, when the aerial vehicle lands ata delivery location, relay location and/or materials handling facility,the aerial vehicle may engage with a charging member at the locationthat will recharge and/or replace the power module.

As mentioned above, the aerial vehicle 101 may also include a payloadengagement mechanism 113. The payload engagement mechanism 113 may beconfigured to engage and disengage items and/or containers that holditems. In this example, the payload engagement mechanism 113 ispositioned beneath the body of the aerial vehicle 101. The payloadengagement mechanism may be of any size sufficient to securely engageand disengage containers that contain items. In other implementations,the payload engagement mechanism may operate as the container,containing the item(s). The payload engagement mechanism 113communicates with (via wired or wireless communication) and iscontrolled by the aerial vehicle control system. The aerial vehiclecontrol system is discussed in further detail below with respect to FIG.20.

While the implementations of the aerial vehicle discussed herein utilizepropellers to achieve and maintain flight, in other implementations, theaerial vehicle may be configured in other manners. For example, theaerial vehicle may be a combination of both propellers and fixed wings.In such configurations, the aerial vehicle may utilize one or morepropellers to enable takeoff, landing, and anti-sound generation and afixed wing configuration or a combination wing and propellerconfiguration to sustain flight while the aerial vehicle is airborne. Insome implementations, one or more of the propulsion mechanisms (e.g.,propellers and motors) may have a variable axis such that it can rotatebetween vertical and horizontal orientations.

FIG. 2 is a view of a propulsion mechanism 202 with telescopingpropeller blades 204, according to an implementation. In the illustratedexample, the propulsion mechanism includes a motor 206 and threetelescoping propeller blades 204. In other implementations, thepropulsion mechanism may include fewer or additional telescopingpropeller blades. The motor may be any type of motor that may rotate andcause the propeller blades 204 to rotate, thereby generating a liftingforce. For example, the motor 206 may be a direct current brushlessmotor.

Rather than having a single shaft coupled to and rotated by the motor,the housing 207 of the motor may be rotated by the motor. In such aconfiguration, a shaft 205 of the telescoping propeller blades 204extend through the housing and are configured to be extendable orretractable with respect to the housing. As illustrated, each propellerblade includes a shaft 205-1, 205-2, 205-3 having a proximal end and adistal end. The proximal end of each shaft extends through the housing207 of the motor and the propeller blade 204-1, 204-2, 204-3 of thepropeller is coupled to the distal end of the shaft and extends awayfrom the shaft. The propeller blades generate lifting forces whenrotated by the motor.

While FIG. 2 illustrates a solid shaft that extends or retracts withrespect to the housing 207, in other implementations, the shaft may be atelescoping shaft that is coupled to the housing at a fixed end. In sucha configuration, the opposing end of the shaft may be extended,retracted and/or rotated thereby moving the propeller blade coupled tothe opposing end inward, outward, or rotationally with respect to themotor.

The propulsion mechanism also includes a propeller adjustment controller208 configured to extend and/or retract each of the propeller blades 204by moving the shaft in or out with respect to the motor housing 207. Thepropeller adjustment controller may have multiple differentconfigurations and, in some implementations, each propeller blade may becontrolled by a separate propeller adjustment controller. In otherimplementations, each propeller blade of the propulsion mechanism may becontrolled by a single propeller adjustment controller.

In one implementation, as illustrated in the expanded view 209-1 of FIG.2, the propeller adjustment controller may include a spring that iscoupled to and extends around the shaft 205 and positioned within aninterior of the housing 207 of the motor. As the RPM of the motorincreases and, thus, the centrifugal force acting upon the propellerblade increases, the spring compresses 308 (FIG. 3) between theconnection point with the shaft and the inner wall of the housing 307,thereby allowing the propeller blade to extend away from the housing 307of the motor 306, as illustrated in FIG. 3. In comparison, as the RPM ofthe motor decreases and, thus, the centrifugal force acting upon thepropeller blade decreases, the spring decompresses thereby retractingthe propeller blade 204 toward the housing 207 of the motor 206.

In other implementations, rather than or in addition to using a spring,the propeller adjustment controller may include a series of gears and/oractuators that may be used to mechanically extend and/or retract thepropeller blade. For example, referring to the expanded view 209-2, aportion of the shaft may include a series of gears or grooves 211 thatmate with a gear 212. The gear 212 may be controlled by the propelleradjustment controller and, when rotated in a first direction, the gear212 will cause the propeller blade to extend away from the housing 207of the motor 206. When the gear 212 is rotated in the second direction,the gear 212 will cause the propeller blade to retract toward thehousing of the motor.

In still other implementations, the propeller adjustment controller mayutilize other mechanisms, alone or in combination with springs and/orgears to extend, retract, or otherwise alter a position of the propellerblades 204 of the propulsion mechanism. For example, pistons,hydraulics, pneumatics, etc., may be included in the propelleradjustment controller to alter a position of one or more of thepropeller blades 204 of the propulsion mechanism 202.

The propeller adjustment controller may also be configured to rotate theshaft so that a pitch or angle of attack of the propeller blade 204 isaltered, thereby altering the lift generated by the propeller blade. Forexample, if the propeller adjustment controller rotates the shaft in afirst direction (e.g., clockwise), the pitch and/or angle of attack ofthe propeller blade increases, increasing the lift. If the propelleradjustment controller rotates the shaft in a second direction (e.g.,counter-clockwise), the pitch and/or angle of attack of the propellerblade 204 decreases, decreasing the lift.

As the propulsion mechanism 202 rotates, the propeller blades generate alifting force that is used to aerially navigate the aerial vehicle. Inaddition to generating lift, the propulsion mechanism 202 also generatessound, referred to herein as a sound profile. For example, when thepropeller blades are in a first position and the motor is rotating at afirst RPM, a first sound profile is generated as a result of the airflowaround the rotating propeller blades. As discussed below, this soundprofile may be measured and maintained in a data store by the aerialvehicle control system.

By enabling alteration of the position of the propeller blades and/orthe pitch or angle of attack of the propeller blades, different soundprofiles and/or different lifting forces can be generated at the sameRPM of the motor. For example, if the propeller blades are all fullyextended, the lifting force generated by the propulsion mechanism 202,even at the same RPM, will increase because the velocity of thepropeller blades will increase. Likewise, the generated sound profilewill be altered because of the change in the airflow around thepropeller blades. In comparison, if the propeller blades are retractedtoward the housing 207 of the motor 206 and the RPM of the motor 206remains constant, the velocity of the propeller blades will decrease,thereby decreasing the lifting force and again altering the soundprofile of the propulsion mechanism.

The propulsion mechanism may also include a series of positionablecounterweights 210 that may be adjusted based on the position of one ormore of the propellers. For example, if all the propellers are extendeda same amount and have a similar weight, the counterweights may bedistributed equally around the motor 206 of the propulsion mechanism, asillustrated in FIG. 2. However, if one of the propellers is extendedaway from the motor 206 a distance greater than the distance of one ormore other propellers and/or if one of the propeller blades has a higherweight than other propeller blades, the positionable counterweights maybe shifted about the propulsion mechanism and/or extended from thepropulsion mechanism, as illustrated in FIG. 3, so that the center ofmass of the propulsion mechanism remains balanced. In someimplementations, the position of the counterweights 210 may be known andcorrespond to respective positions of the propellers. Likewise, in someimplementations, one or more sensors may be included in the propulsionmechanism that measure the vibrations and/or moments acting on thepropulsion mechanism 202 and the position of the counterweights 210 maybe adjusted based at least in part on the measurements.

As will be appreciated, for each defined RPM of the motor 206, anynumber of positions of the propeller blades, pitches of the propellerblades, and counter weight positions may be utilized. As such, anynumber of lifting forces and sound profiles may be realized with theimplementations discussed herein. A table that includes the RPM of themotor, a position of each propeller blade, a lifting force of thepropulsion mechanism and a generated sound profile may be maintained bythe aerial vehicle control system and used to select a propeller bladeconfiguration and RPM for the motor in response to a commanded liftingforce. A portion of an example table is illustrated below as Table 1:

TABLE 1 Propeller Propeller Propeller Lifting Sound Blade 1 Blade 2Blade 3 Force Profile RPM Position Position Position (Newton) (Decibels)2,300 RPM 1 1 1 190 N 70 dB 2,300 RPM 3 2 2 195 N 75 dB 2,300 RPM 5 3 3202 N 80 dB 2,300 RPM 5 5 5 230 N 85 dB

In the example portion of illustrated Table 1, the RPM of the motor isheld constant and the propeller blades are moved to different positions,thereby generating different lifting forces and sound profiles. In thisexample, the different positions of the propeller blades range betweenfully retracted toward the housing of the motor, represented as position1, to fully extended from the housing of the motor, represented asposition 5. As will be appreciated, any number of positions between afully retracted position and a fully extended position may be utilizedand the positions 1-5 are provided for example and discussion purposesonly. In addition to positions, the table may also identify differentconfigurations for each propeller blade (e.g., pitch, camber, angle ofattack, chord length) and/or different counterweight positions.

The propeller blades of the propulsion mechanism may be moved betweenpositions and one or more of the propeller blades may be in a differentposition than the other propeller blades and/or have differentconfigurations than other propeller blades of the propulsion mechanism.In such a configuration, to maintain balance of the propulsionmechanism, the weight distribution of the propeller blades needs toremain centered and the center of lift needs to remain centered.Accordingly, based on the position of the propeller blades, one or moreof a configurations of the propeller blades may be altered, therebyaltering the lift. Likewise, a position of one or more of thecounterweights 210 may be altered, thereby altering the weightdistributions around the propulsion mechanism.

FIG. 3 illustrates the propulsion mechanism 300 in which the firstpropeller blade has been fully extended such that the shaft 305-1 ismoved outward from the housing 307 of the motor and the propeller blade304-1 is extended away from the housing 307 of the motor. Referring toTable 1 above, the first propeller is in the fifth position. To balancethe propulsion mechanism 300 and generate the desired lift and soundprofile, the other two propeller blades are partially extended toposition three. For example, the propeller blade 304-2 and the propellerblade 304-3 are each partially extended from the housing of the motor306. Likewise, the counterweights 310 are rotated to be on the oppositeside of the housing 307 so that the overall weight remains centered inthe propulsion mechanism. Likewise, as illustrated, some of thecounterweights 310 have been extended away from the housing 307 of themotor 306. In addition, the pitch of the propeller blade 304-1 may bedecreased, thereby reducing the lift generated by the propeller bladeand/or the pitch of propeller blades 304-2 and 304-3 may be increased,thereby increasing the lift generated by those propeller blades. Bydecreasing the lift generated by propeller blade 304-1 and/or increasingthe lift generated by 304-2 and 304-3, the total lifting force generatedby the propulsion mechanism remains centered about the propulsionmechanism.

In propulsion mechanisms in which the distance at which the propellerblades are extended are not all the same, the sound profile may bealtered. For example, blade vortex interaction (“BVI”), which is soundgenerated when a propeller blade passes close to trailing tip vorticespreviously generated by another propeller blade of the propulsionmechanism, may be reduced. This reduction may occur, for example,because a propeller blade that is retracted may not pass through thevortices shed from the tip of a propeller that is extended a furtherdistance. Likewise, because the blade tip velocity and/or pitch (orother characteristics) of the propeller blades may vary at the differentextensions, the sound profile generated by the propeller blades may bedifferent, even when rotating at the same RPM. As such, a soundgenerated by a first propeller of the propulsion mechanism may causeinterference with a sound generated by a second propeller of thepropulsion mechanism.

FIG. 4 is another view of a propulsion mechanism 400 with telescopingpropeller blades, according to an implementation. In this example, thepropeller blades are fully retracted toward the housing 407 of the motor406 and the counterweights 410 are evenly distributed about the housing407. Referring to Table 1 above, the position illustrated in FIG. 4corresponds to each of the propeller blades being at position 1. Becauseeach of the propeller blades 404-1, 404-2, and 404-3 are extended a samelength from the housing 307 of the motor 306, the propulsion mechanismis in balance, generates a lifting force, and a sound profile that isknown for this position of the propeller blades. As shown, when thepropeller blades are retracted, the propeller blades 404-1, 404-2, and404-3 are retracted toward the housing 407 of the motor. Likewise, theshaft 405-1, 405-2, and 405-3 of each propeller is retracted back andextending out an opposing side of the housing of the motor 406.

FIG. 5 is another view of a propulsion mechanism 500 with telescopingpropeller blades, according to an implementation. In this example, allthree of the propeller blades 504-1, 504-2, and 504-3 are fully extendedfrom the housing 507 of the motor 506 and the counterweights 510 areevenly distributed about the housing 507. Referring to Table 1 above,the position illustrated in FIG. 5 would correspond to each of thepropeller blades being at position 5. Because each of the propellerblades are extended a same length from the housing 507 of the motor 506,the propulsion mechanism is in balance, generates a lifting force and asound profile that is known for this position of the propeller blades.As shown, when the propeller blades are fully extended, the propellerblades 504-1, 504-2, and 504-3 are extended away from the housing 507 ofthe motor 506. Likewise, the shaft 505-1, 505-2, and 505-3 of eachpropeller is extended and near the opposing side of the housing 507 ofthe motor.

FIG. 6 is a view of a propulsion mechanism 600 with different propellerblades coupled to a hub 607, according to an implementation. As withtypical propulsion mechanism configurations, the hub 607 of thepropeller is coupled to and rotated by a motor 606. However, in thisimplementation, rather than each propeller blade of the propeller havinga uniform configuration, the different propeller blades 604-1, 604-2,and 604-3 have different configurations. For example, the differentpropeller blades may have one or more of a different size, shape,length, pitch, camber, chord length, weight, etc.

In configurations in which the propeller blades are different, to keepthe propulsion mechanism in balance during operation the center ofgravity of the propulsion mechanism 600 and the center of lift of thepropulsion mechanism need to remain centered with respect to arotational center of the propulsion mechanism. In this example, therotational center of the propulsion mechanism is a center of the motor606 about which the hub 607 is connected. To maintain the center ofgravity at the center of the motor 606, the weight distribution of thepropeller blades 604 is approximately equal. For example, the largestpropeller blade may be formed of a first material, the mid-sizedpropeller blade 604-2 may be formed of a second material, the smallestpropeller blade 604-3 may be formed of a third material, each of thematerials having different weights so that the total weight distributionand center of gravity remains centered about the motor 606. In otherimplementations, the propeller blades may all be formed of the samematerial, but have different thicknesses, weight distributions along thelength of the propeller blades, etc., so that the center of gravityremains centered about the motor 606. In still other examples, in amanner similar to that discussed above with respect to FIGS. 2-5, one ormore counterweights may be included in the propulsion mechanism 600 tocounterbalance one or more of the propeller blades 604 so that theweight distribution remains balanced and the center of gravity remainscentered at the motor 606.

In addition to balancing the weight distribution of the different sizedpropeller blades, the individual lifting forces of each propeller blade604 is configured to be approximately equal at a same RPM so that thecenter of lift is at approximately the center of the motor 606. Tobalance the individual lifting forces of the different propeller blades604, each of which are rotated at the same RPM by the motor, the pitch,angle of attack, camber, chord line, thickness, etc. may be differentfor each propeller blade so that the individual lifting forces generatedby each of the propeller blades 604 results in the center of lift beingcentered with respect to the motor 606. For example, the largestpropeller blade 604-1 may have the lowest pitch and the smallestpropeller blade 604-3 may have the highest pitch so that the respectivelifting forces are balanced.

Similar to the discussion above with respect to FIG. 3, with differentpropeller blades, different sound profiles may be generated and thesound generated from BVI may be reduced because some of the propellerblades may not pass through vortices shed from the tips of otherpropeller blades of the propeller. For example, propeller blade 604-3,which is the smallest propeller blade of the propulsion mechanism 600,may not pass through the vortices shed from the tip of the largestpropeller blade 604-1 due to the difference in length of the propellerblades. Likewise, in some implementations, the propeller bladeconfigurations of each of the propeller blades 604-1, 604-2, and 604-3may be optimized to generate respective sound profiles at a defined RPMso that the respective sound profiles will cause interference with eachother thereby altering the net effect sound generated by the propulsionmechanism.

As will be appreciated, while the example discussed above with respectto FIG. 6 illustrates three propeller blades of a propulsion mechanism,in other implementations there may be fewer or additional propellerblades of the propulsion mechanism. Likewise, some of the propellerblades may have the same configuration. Moreover, in someimplementations, the configuration of the propeller blades may beadjustable as discussed above with respect to FIGS. 2-5. For example,returning briefly to FIG. 2, one or more of the propeller blades 204-1,204-2, or 204-3 may have a different configuration than other propellerblades of the propulsion mechanism.

In some implementations, as an alternative to or in addition to alteringthe position of a propeller blade and/or altering an angle of attack orpitch of the propeller blade by rotating the shaft of the propellerblade, as discussed above, the physical characteristics (e.g., shape,thickness, camber, chord length, etc.) may be altered during operationof the aerial vehicle. Such alterations may further change the liftingforce generated by the propeller blade, the efficiency of the propellerblade, and/or the sound profile of the propeller blade.

For example, FIG. 7 is a top-view and a side-view of a propeller blade700 that includes a propeller blade treatment 702-1, according to animplementation. In this example, the propeller blade treatment 702-1 isan inflatable bladder that extends along the leading edge 705 of thepropeller blade. When the propeller blade treatment 702-1 is in a firstposition, it is deflated and retracted against the leading edge 705 ofthe propeller blade such that it is substantially in line with thepropeller blade, as illustrated in FIG. 7.

To alter the position of the propeller blade treatment 702 from thefirst position, illustrated in FIG. 7, to a second position, illustratedin FIG. 8, the propeller adjustment controller 711 causes the propellerblade treatment 702-1 to inflate. When the propeller blade treatmentinflates, it expands in a direction that includes a vertical and/orhorizontal component with respect to the surface area 709 of thepropeller blade 700. For example, as illustrated in the side view ofFIG. 8, the propeller blade treatment 802-1 expands out of the plane ofthe surface area 809 of the propeller blade 800. This altered shape ofthe propeller blade disrupts the airflow as it passes over the propellerblade, thereby changing the sound generated by the propeller blade, thelifting force generated by the propeller blade and/or the efficiency ofthe propeller blade.

The propeller blade treatment 702, 802 illustrated in FIGS. 7-8 may beof any type of expandable or flexible material. Likewise, while thisexample illustrates the propeller blade treatment 702 extending alongthe leading edge, in other implementations, the propeller bladetreatment 702 may be at other positions and/or orientations along thepropeller blade. For example, the propeller blade treatment 702 mayextend and cover the top surface area of the propeller blade. In such anexample, when the propeller blade treatment is inflated, the thicknessof the propeller blade increases, and the camber of the propeller bladechanges.

When the propeller blade treatment is moved between a first position anda second position, even at the same RPM, the propeller will generatedifferent sounds when the propeller blade treatment is at the differentpositions. In this example, the propeller blade may be capable ofgenerating multiple different sounds and lifting forces as it rotates,depending on the amount of inflation of the propeller blade treatment702-1. For example, the propeller blade 700 may generate a first soundand a first lifting force when rotating at a defined RPM and thepropeller blade treatment 702-1 is in a first position (e.g., notinflated), generate a second sound and second lifting force whenrotating at the same RPM and the propeller blade treatment 702-1 is in asecond position (e.g., 50% inflated), and generate a third sound andthird lifting force when the propeller is rotating at the same RPM andthe propeller blade treatment 702-1 is in a third position (e.g., 100%inflated). By varying the amount of inflation, and thus the shape of thepropeller blade, different sounds and/or lifting forces may be generatedby the propeller blade 700 as the propeller rotates.

In some implementations, as illustrated in FIGS. 9A-9C, the airfoilshape, camber, and/or chord length of the propeller blades of apropeller may be dynamically adjustable, according to an implementation.For example, the propeller blade 903 may be substantially hollow, e.g.,with a solid skin defining an airfoil having a hollow cavity therein,with one or more internal supports 901, 902, 905 or structural featuresfor maintaining and/or altering the shape of the airfoil. For example,the propeller blade 903 or portions thereof may be formed from durableframes of stainless steel, carbon fibers, or other similarlylightweight, rigid materials and reinforced with radially aligned fibertubes or struts. Utilizing a propeller blade 903 having a substantiallyhollow cross-section thereby reduces the mass of the lifting propellerand enables wiring, cables and other conductors or connectors to bepassed there through, and in communication with one or more othercontrol systems components or features. Likewise, the support arms, suchas the spine 901, trailing edge ribs 902, and/or leading edge ribs 905may be adjustable to thereby alter a shape of the airfoil. For example,referring to FIG. 9B, which illustrates a cross-sectional view of thespine 901 of FIG. 9A, when the spine 911 is in a first position, leadingedge ribs 915-1, and trailing edge ribs 912-1 are in a first positionand the airfoil shape of the propeller blade 913, which is across-sectional view of the blade 903 (FIG. 9A), has a first shape. Ifthe airfoil shape of the blade is to be altered, the spine 901 may berotated, as illustrated in FIG. 9C. In this example, the spine 921,which is a cross-sectional view of the spine 901 (FIG. 9A), is rotated,which causes the leading edge rib 925-1 and trailing edge rib 922-1 tobend or curve due to the forces acting on the support arms from theexternal solid skin of the propeller blade 923. As the ribs 922-1, 925-1bend or curve, the airfoil shape of the propeller blade 923, which is across-section view of the blade 903, also changes. Specifically, thecamber and chord length of the propeller blade is altered.

Returning to FIG. 9A, depending on the quantity, shape and/or positionof the ribs 902 and 905, and the couple points between the leading edgeribs 905 and/or trailing edge ribs 902 with the spine 901, the airfoilshape of the blade 903 may be different at different sections of thepropeller blade. As illustrated, any number of trailing edge ribs 902-1,902-2-902-N may be included in the propeller blade 903 and define theairfoil shape of a portion of the propeller blade 903 depending on thecurvature of the trailing edge ribs 902 and the position along the spine901 to which they are coupled. Likewise, as illustrated, any number ofleading edge ribs 905-1, 905-2-905-N may be included in the propellerblade 903 and define the airfoil shape of a portion of the propellerblade 903 depending on the curvature of the leading edge ribs 905 andthe position of the spine 901 to which they are coupled. The quantity,size, shape, position, etc., may vary between trailing edge ribs 902and/or leading edge ribs 905.

FIG. 10 illustrates a view of another adjustable propeller blade 1002 inwhich a chord length of the propeller blade may be altered duringoperation, according to an implementation. Similar to the propellerblade discussed with respect to FIGS. 9A-9C, the propeller blade 1002may be substantially hollow, e.g., with a solid skin defining an airfoilhaving a hollow cavity therein. For example, the propeller blade 1002,or portions thereof, may be formed from durable frames of stainlesssteel, carbon fibers, or other similarly lightweight, rigid materialsand reinforced with radially aligned fiber tubes or struts.

In this example, the propeller adjustment controller includes apositionable flap 1006 that may be moved between a retracted positionand an extended position. When the positionable flap is in the retractedposition, as illustrated by propeller blade 1002-1, the positionableflap 1006 is retracted into the substantially hollow portion of thepropeller blade 1002-1 so that the surface area and chord length of thepropeller blade is defined by the leading edge 1004 of the propellerblade 1002, the trailing edge 1005 of the propeller blade 1002 and thesurface area 1007 of the propeller blade.

To move the positionable flap 1006 from the retracted position to theextended position, as illustrated by propeller blade 1002-2, thepropeller adjustment controller 1011 sends instructions that cause thepositionable flap to extend beyond the trailing edge 1005 of thepropeller blade by a defined amount. When the positionable flap 1006 isin the extended position, the surface area and chord length of thepropeller blade are increased because the positionable flap extendsbeyond the trailing edge 1005 of the propeller blade. Essentially, thepositionable flap becomes an extension of the propeller blade 1002. Thisincreased surface area and chord length of the propeller blade resultsin increased lift by the propeller blade 1002, alters the sound profilegenerated by the propeller blade and, in some instances, alters theefficiency of the propeller blade 1002.

The positionable flap 1006 may be formed of any substantially rigidmaterial, a flexible material, or a combination of rigid and flexiblematerials. For example, the positionable flap 1006 may include asubstantially rigid core that is covered with a flexible material thathelps dampen sound generated as air passes over the positionable flapwhen the positionable flap is in the extended position, as illustratedby propeller blade 1002-2.

FIG. 11 illustrates a view of an adjustable propeller 1102, according toan implementation. In this example, the adjustable propeller 1102includes two propeller blades 1105-1, 1105-2 extending from a hub 1106.Each of the two propeller blades 1105-1, 1105-2 includes a plurality ofadjustable sections that may be moved by the propeller adjustmentcontroller that controls the configuration of the propeller 1102. Inthis example, the first propeller blade 1105-1 includes seven adjustablesections 1104-1, 1104-2, 1104-3, 1104-4, 1104-5, 1104-6, and 1104-7 andthe second propeller blade 1105-2 includes an equal number of adjustablesections 1104-8, 1104-9, 1104-10, 1104-11, 1104-12, 1104-13, and1104-14. In other implementations, the different propeller blades mayhave a different quantity of adjustable sections and/or some of theadjustable sections may have different sizes and/or shapes.

The different adjustable sections 1104 are arranged in a stackedconfiguration such that the propeller blades may be adjusted between anextended or fanned out position, as illustrated by propellerconfiguration 1102-1, and a vertically stacked position, as illustratedby propeller configuration 1102-3. The propeller adjustment controllermay function to pivot or rotate different sections about the hub 1106 toform different propeller blade configurations. In the illustratedexample, the two propeller blades are formed of joined sections so thatthe propeller adjustment controller can adjust one section of the firstpropeller blade 1105-1, which will result in the corresponding coupledsection of the second propeller blade 1105-2 adjusting in a similarmanner so that the overall configuration and balance of the propeller ismaintained. In other implementations, each section of each propellerblade may be independently adjustable by the propeller adjustmentcontroller.

Turning first to propeller configuration 1102-1, which illustrates thepropeller configuration 1102-1 in a fanned out or extended position,each of the adjustable sections have been rotated about the hub, so thatthey are exposed forming a large surface area of the propeller blades.In this configuration, the propeller blades 1105-1 and 1105-2 have alargest chord length and generate a largest amount of lifting force.However, the sound profile in the configuration illustrated by propellerconfiguration 1102-1 may also be the loudest at a given RPM and thepropeller configuration may consume the largest amount of power due tothe increased surface area. However, because of the increased liftgenerated by the configuration 1102-1, the RPM of the motor rotating thepropeller may be decreased, thereby reducing the sound generated by thepropeller configuration 1102-1. As such, the propeller configuration1102-1 may be useful during final descent toward a delivery destinationor initial ascent from a delivery destination because the needed liftingforce can be generated at a lower RPM because of the increased surfacearea. Rotating the propeller at the lower RPM reduces the soundgenerated by the propeller. Likewise, the larger surface area willgenerate more of a broadband noise, which is similar to white noise.Broadband noise is often found to be more appealing and/or acceptable tohumans and/or other animals. Overall, the propeller configuration 1102-1optimizes for sound because it allows a desired lift to be generated ata lower RPM, and produces a more appealing sound.

In comparison, propeller configuration 1102-2 illustrates aconfiguration in which adjustable sections 1104-5, 1104-6, and 1104-7have been moved to a stacked position with respect to adjustable section1104-4, and adjustable sections 1104-12, 1104-13, and 1104-14 have beenmoved to a stacked position with respect to adjustable section 1104-11.When partially stacked, as illustrated, the propeller blades 1105-1,1105-2 of the propeller configuration 1102-2 have a smaller chord lengthand generate less lifting force, at the same RPM, compared to thepropeller configuration 1102-1. Yet, because of the decreased surfacearea, the propeller configuration 1102-2 also consumes less power thanthe propeller configuration 1102-1. Specifically, when generatingapproximately the same lifting force as in 1102-1 using propellerconfiguration 1102-2, which will require a higher RPM for propellerconfiguration 1102-2, will consume less power than the propellerconfiguration 1102-1. Likewise, the sound generated by the propellerconfiguration 1102-2 is less than the sound generated by the propellerconfiguration 1102-1 when the propellers are rotated at the same RPM.However, the sound generated by the propeller configuration 1102-2 issomewhat more than the sound generated by the propeller 1102-1 whenrotated at different a RPM to generate approximately the same amount oflift. Accordingly, the propeller configuration 1102-2 may be useful asan aerial vehicle begins to descend, for example, toward a deliverydestination but has not reached a final descent altitude, ascends fromthe delivery destination but is above a defined altitude, and/or duringtransit when the sound generated by the aerial vehicle is not a primaryconcern. In addition, the propeller configuration 1102-2 provides moreagility and maneuverability of the aerial vehicle than propellerconfiguration 1102-1 because of the lower surface area of the propellerconfiguration 1102-2.

Overall, the propeller configuration 1102-2 optimizes for efficiency(i.e., reduced power consumption), even though it requires higher RPM togenerate the same lift as propeller configuration 1102-1 and produces ahigher sound output at the higher RPM.

Finally, propeller configuration 1102-3 illustrates a configuration inwhich all of the adjustable sections of the propeller blades are in astacked configuration. For example, adjustable sections 1104-2, 1104-3,1104-4, 1104-5, 1104-6, and 1104-7 are all vertically stacked withrespect to adjustable section 1104-1. The tips of adjustable sections1104-2, 1104-3, and 1104-4 are visible because those adjustable sectionsare longer than the adjustable section 1104-1. However, the tips ofadjustable sections 1104-5, 1104-6, and 1104-7 are not visible becausethey are shorter in length than adjustable section 1104-4 and arevertically stacked beneath adjustable section 1104-4. Similarly,adjustable sections 1104-9, 1104-10, 1104-11, 1104-12, 1104-13, and1104-14 are all vertically stacked with respect to adjustable section1104-8. The tips of adjustable sections 1104-9, 1104-10, and 1104-11 arevisible because those adjustable sections are longer than the adjustablesection 1104-8. However, the tips of adjustable sections 1104-12,1104-13, and 1104-14 are not visible because they are shorter in lengththan adjustable section 1104-11 and are vertically stacked beneathadjustable section 1104-11.

In the propeller configuration 1102-3, the propeller produces the leastamount of lift at the same RPM compared to the propeller configurations1102-2 and 1102-1 but also consumes the least amount of power because ofthe reduced surface area of the propeller configuration 1102-3.Likewise, the aerial vehicle when operating with the propellerconfiguration 1102-3 may be more agile and maneuverable, again becauseof the reduced surface area compared to the surface areas of propellerconfigurations 1102-1 and 1102-2. However, to produce approximately asame amount of lift as either propeller configuration 1102-1 or 1102-2,the RPM must be higher for propeller configuration 1102-3. The higherRPM cause the propeller configuration 1102-3 to consume mower power andgenerate more sound than either propeller configuration 1102-1 or1102-2. As such, the propeller configuration 1102-3 is optimized foragility.

In some implementations, the propeller configuration 1102-3 may be usedwhen the aerial vehicle is in transit flight and using other liftingmechanisms (e.g., wings) to maintain flight rather than using thepropulsion. Specifically, the propeller may be adjusted to propellerconfiguration 1102-3, which has the least amount of surface area of theconfigurations available for the propeller, and orient and lock thepropeller in a direction of flight, thereby reducing drag produced bythe propeller when the propeller is not in operation.

The adjustable sections of the propeller blades may be formed of anysuitable material, such as carbon fiber. In some implementations, theadjustable sections may be formed of a flexible material or a memorymetal that will take a particular shape when electrically charged.Likewise, in some implementations, the material may flex or bend into aparticular shape when in the fanned or expanded position so that theexposed sections of the propeller blade align to form an airfoil shape.In comparison, when the adjustable section is vertically retracted withrespect to another adjustable section, the flexible material may move tofollow the curvature or shape of the adjacent adjustable section so thatthe profile of the stacked adjustable sections is reduced, therebyreducing drag.

The example illustrated in FIG. 11 shows three different positions orconfigurations that may be formed with the propeller 1102, representedas propeller configurations 1102-1, 1102-2, and 1102-3. However, it willbe appreciated that additional configurations may be produced with theadjustable sections of the propeller 1102. For example, some of theadjustable sections may be exposed while others are vertically stacked.

FIG. 12A provides an illustration of yet another propeller configurationthat may be formed with an adjustable propeller 1202, according to animplementation. In this example, referring first to the first propeller1205-1, adjustable sections 1204-1 and 1204-2 are vertically stacked andpivoted to a first position with respect to the hub 1207, adjustablesections 1204-3 and 1204-4 are vertically stacked and pivoted to asecond position with respect to the hub 1207, and adjustable sections1204-5, 1204-6, and 1204-7 are vertically stacked and pivoted to asecond position with respect to the hub 1207. In a similar manner,referring to the second propeller blade 1205-2, adjustable sections1204-8 and 1204-9 are vertically stacked and pivoted to a fourthposition with respect to the hub 1207, adjustable sections 1204-10 and1204-11 are vertically stacked and pivoted to a fifth position withrespect to the hub 1207, and adjustable sections 1204-12, 1204-13, and1204-14 are vertically stacked and pivoted to a sixth position withrespect to the hub 1207.

In the illustrated configuration, the adjustable sections of thepropeller 1202 have essentially been arranged to form six differentpropeller blades, each of the propeller blades generate a lifting force.Likewise, the positioning of the adjustable sections may be varied, asillustrated, or equally distributed about the hub 1207.

FIG. 12B provides another illustration of a propeller configuration thatmay be formed with an adjustable propeller 1212, according to animplementation. In this example, similar to FIG. 12A, adjustablesections 1214-1 and 1214-2 are vertically stacked and pivoted withrespect to the hub 1217, adjustable sections 1214-3 and 1214-4 arevertically stacked and pivoted with respect to the hub 1217, andadjustable sections 1214-5, 1214-6, and 1214-7 are vertically stackedand pivoted with respect to the hub 1217. In a similar manner,adjustable sections 1214-8 and 1214-9 are vertically stacked and pivotedwith respect to the hub 1217, adjustable sections 1214-10 and 1214-11are vertically stacked and pivoted with respect to the hub 1217, andadjustable sections 1214-12, 1214-13, and 1214-14 are vertically stackedand pivoted with respect to the hub 1217.

In the illustrated configuration, the adjustable sections of thepropeller 1212 have essentially been arranged to form six differentpropeller blades, each of the propeller blades generating a liftingforce. In comparison to the configuration illustrated with respect toFIG. 12A, the propeller configuration 1212 includes distributing theadjustable sections approximately equally about the hub 1217. Forexample, because there are six adjustable sections, each section ispositioned at approximately sixty degrees with respect to the nextsection.

FIG. 13 depicts a view of another aerial vehicle configuration,according to an implementation. The body 1304 of the aerial vehicle 1300may be formed of any suitable material, such as graphite, carbon fiber,aluminum, titanium, etc., or any combination thereof. In this example,the body 1304 of the aerial vehicle 1300 is a single carbon fiber frame.The body 1304 includes a hub 1306, propulsion mechanism arms 1308,propulsion mechanism mounts 1311, and a perimeter protective barrier1314. In this example, there is a single hub 1306 and four propulsionmechanism arm sets 1308 that extend from the hub 1306 to a propulsionmechanism mount 1311 and then extend to a perimeter protective barrier1314.

Within each section of the motor arms is a propulsion mechanism 1316. Inthe illustrated aerial vehicle 1300 configuration, the aerial vehicle1300 includes four sets of propulsion mechanisms 1316-1, 1316-2, 1316-3,and 1316-4. In this configuration, each propulsion mechanism includestwo motors and two propellers that are coaxially aligned. For example,as illustrated by the expanded view of propulsion mechanism 1316-1, thepropulsion mechanisms include an upper motor 1316-1A that is coupled toa motor arm on the upper side of the aerial vehicle and a lower motor1316-1D that is coupled to a motor arm on the lower side of the aerialvehicle. The upper motor 1316-1A and the lower motor 1316-1D arevertically aligned.

The upper motor 1316-1A includes a first shaft 1316-1E that extendsdownward toward the lower motor 1316-1D, and the lower motor 1316-1Dincludes a second shaft 1316-1F that extends upward toward the uppermotor 1316-1A. Coupled to the first shaft is a first propeller 1316-1Bthat is rotated by the first shaft 1316-1E when the first shaft 1316-1Eis rotated by the upper motor 1316-1A. Coupled to the second shaft is asecond propeller 1316-1C that is rotated by the second shaft 1316-1Fwhen the second shaft 1316-1F is rotated by the lower motor 1316-1D.

The propellers 1316-1B, 1316-1C, even though coupled to differentshafts, are coaxially aligned. In addition, the propellers are separatedby a distance d₁. Likewise, rather than counter-rotating the propellers1316-1B, 1316-1C, during some modes of operation the propellers may bein rotational phase alignment and rotated in the same direction(co-rotated).

Selecting a distance d₁, rotationally phase aligning, and co-rotatingthe coaxially aligned propellers is done to reduce or otherwise altersound generated by the high-pressure pulse of the induced flow from therotation of the propellers. Induced flow is the airflow that is forcedthrough a propeller and moving in the same or similar direction alongthe axis of the shaft that is rotating the propeller. The induced flowis caused by the deflection of air by the passage of a propeller blade.Induced flow moves downward away from the propeller in a spiral patterndue to the rotation of the propeller blade, creating a sinusoidalwaveform at the perimeter of the induced flow. The induced flow includesa high-pressure pulse generated from the tip and other portions of thepropeller blade that generate the sound heard from the rotation of thepropeller blades. The high-pressure pulse represents a sinusoidalwaveform as it spirals down and away from the propeller.

The distance d₁ is selected so that the waveform of the high-pressurepulse induced flow resulting from the rotation of the first propeller1316-1B is substantially out-of-phase (e.g., having polarities that arereversed with respect to polarities of the predicted sounds) to thewaveform of the high-pressure pulse of the induced flow resulting fromthe rotation of the second propeller 1316-1C, when the first propeller1316-1B is in rotational phase alignment with the second propeller1316-1C. In some implementations, the rotational phase alignment of thetwo propellers with respect to each other may be adjusted so that thetwo waveforms cause destructive interference with one another, therebyreducing the sound from the high-pressure pulses.

By positioning the two coaxially aligned propellers so that theresulting waveforms are out-of-phase, the waveforms cause interferencethat results in at least a portion of the sound generated by thehigh-pressure pulses of the induced flows from the two propellers beingaltered. For example, the interference may be destructive interferencethat causes at least a portion of the two sounds to be canceled out orotherwise altered.

The aerial vehicle control system 1310 may be mounted to the body of theaerial vehicle and one or more components (e.g., antenna, camera,gimbal, radar, distance-determining elements) may be mounted to thebody, as discussed above.

FIG. 14 depicts an illustration of induced flows from a propulsionmechanism 1400 that includes two coaxially aligned propellers 1403,1406, according to an implementation. For ease of discussion, the motorand other components have been eliminated from the illustration in FIG.14. As illustrated, the lower propeller 1403 and the upper propeller1406 are phase aligned, both rotate about a shaft 1404 in a clockwisedirection, and both generate an induced flow that progresses downwardaway from the propellers.

Coaxially stacked propellers are considered to be phase aligned whenthere is approximately no offset between the two propellers. Forexample, the two propellers 1403 and 1406 are in rotational phasealignment because the propeller blades are aligned so that if viewingthe propellers from a top-down perspective you would only be able to seethe upper propeller 1406. For coaxially stacked propellers having thesame design, any arbitrary feature (e.g., leading edges, blade centers,trailing edges, etc.) of the two (or more) propellers may be aligned toachieve phase alignment. However, in circumstances where one or morepropellers differ, “phase alignment” may differ depending on whichparticular feature is being used as a reference point. Thus, for twocoaxial but distinct propeller designs, a phase alignment based uponleading edges may differ from phase alignment based upon blade center ortrailing edges. Thus, for purposes of specificity, the term “phasealignment” may be modified to be described as “leading edge phasealignment,” “trailing edge phase alignment,” or “blade center phasealignment” when the two propellers have different designs, features,and/or configurations. It should be understood by those having ordinaryskill that any number of phase alignments may be described and used andthat the present disclosure is not limited to alignments based solelyupon leading edges, trailing edges, or blade centers.

By phase aligning the coaxially aligned propellers and separating them adefined distance, the waveform generated by the upper propeller 1406will be substantially inverted, or out-of-phase from the waveformgenerated by the lower propeller 1403. The destructive interference ofthe combined waveforms alters the sound generated by the propulsionmechanism. In selected implementations, the defined distance betweenpropellers 1403 and 1406 may be calculated based upon the propellergeometry and computational analysis (e.g., computational fluid dynamicsor finite element analysis). In other implementations, the distancebetween propellers may be determined experimentally by adjusting thecoaxial spacing of the propellers to alter the sound generated to a moredesirable state. In the latter method, audio sensors may be used toprovide real-time feedback as the aerial vehicle (e.g., 1300 of FIG. 13)is operated.

In this example, the clockwise rotation of the lower propeller 1403generates an induced flow 1408 that moves away from the lower propeller1403 in a spiral pattern. Likewise, the clockwise rotation of the upperpropeller 1406 generates an induced flow 1410 that also moves away fromthe upper propeller 1406 in a spiral pattern. Because the lowerpropeller 1403 and the upper propeller 1406 are coaxially aligned,rotationally phase aligned, and separated by a defined distance, thewaveform or high-pressure pulse of the induced flow 1410 from the upperpropeller 1406 causes destructive interference with the waveform orhigh-pressure pulse of the induced flow 1408 from the lower propeller1403, thereby reducing the sound resulting from the rotation of thepropulsion mechanism 1400.

While this example illustrates the induced flow waveforms forming offthe tips of the propellers 1403, 1406, it will be appreciated thatinduced flow waveforms are generated from all segments of the propellerblades at different amplitudes. By offsetting and aligning thepropellers in the manner discussed herein, the waveforms generated byeach segment of the propellers cause destructive interference and reducegenerated sound. Describing the implementations with respect to theinduced flow generated from the tips of the propeller blades is for easeof discussion only and it will be appreciated that the implementationsare equally applicable to reducing sound generated from waveformsgenerated along any portion of the propellers as the propellers rotate.

FIGS. 15A-15B depict the propulsion mechanism 1500 with a motor 1502, alower propeller 1503, and an upper propeller 1506, according to animplementation. In the example illustrated in FIG. 15A, the lowerpropeller 1503 and the upper propeller are coupled to a fixed lengthshaft 1504 and separated a distance d₁. The distance d₁ may be selectedbased on the operating characteristics of the propulsion mechanism 1500.For example, a rotational speed may be determined at which thepropulsion mechanism is operating within its most efficientpower-to-lift range. Likewise, the pitch of the propeller blades and theresulting waveform generated at that rotational speed may be determinedfor the lower propeller 1503 and the upper propeller 1506. Based on thedetermined waveforms, the distance d₁ may be selected that will cause awaveform from the upper propeller 1506 to be substantially out-of-phasewith the waveform from the lower propeller 1503.

In some implementations, the same propeller size and shape may be usedfor the upper propeller 1506 and the lower propeller 1503 so that thegenerated waveforms and induced flows are symmetrical. However, in otherimplementations, because of the altered shape of the airflow passingthrough the lower propeller 1503, due to the induced flow generated bythe upper propeller 1506, the waveform of the lower propeller 1503 maybe different. In such an example, the pitch, size, shape and/or othercharacteristics of either, or both, the upper propeller 1506 and thelower propeller 1503 may be altered so that the waveforms haveapproximately the same period and amplitude. For example, FIG. 16,discussed below, illustrates a configuration of coaxially alignedpropellers in which each propeller has a different size andconfiguration.

In still other implementations, in addition to separating the upperpropeller 1506 and the lower propeller 1503 a defined distance d₁, therotational phase alignment of the propeller blades may be offset adefined amount so that the combination of the distance d₁ and thealignment offset of the propeller blades results in the waveform of theinduced flow from the upper propeller 1506 to be substantiallyout-of-phase from the induced flow from the lower propeller 1503.

In the example illustrated in FIG. 15B, the lower propeller 1513 and theupper propeller 1516 are coupled to an adjustable length shaft 1514. Asillustrated in the expanded view, the adjustable shaft may be adjustedradially (extended or retracted) or rotationally (clockwise orcounter-clockwise). In some implementations, a sensor 1517, such as amicrophone, may be affixed to the motor arm 1515 to which the propulsionmechanism 1550 is attached. The sensor 1517 may measure sound generatedby the propulsion mechanism and the shaft may be adjusted so that thewaveforms of the high-pressure pulses from the induced flow generated byeach of the propellers 1513, 1516 are out-of-phase and cause destructiveinterference, thereby reducing the generated sound. For example, theshaft may be radially extended a distance d₂ to increase the separationof the lower propeller 1513 and the upper propeller 1516. As the shaftis extended, the sensor may continue to measure the generated sound andprovide feedback to the aerial vehicle control system indicating whetherthe sound is increasing or decreasing. The shaft may continue to beextended until the sound stops decreasing. Alternatively, the shaft maybe contracted and the sound measured by the sensor 1517 to determinewhen to stop contracting the shaft 1514.

In addition to extending or contracting the shaft 1514, the alignment ofthe propellers 1513, 1516 may be adjusted by rotating the upper portionof the shaft 1514-2 with respect to the lower portion of the shaft1514-1. Adjusting the rotational phase alignment of the propellers 1513,1516 may be done in addition to or as an alternative to adjusting thedistance between the propellers 1513, 1516. For example, once a distancebetween the propellers is determined at which the generated sound is ata minimum for that rotational speed of the propulsion mechanism, therotational phase alignment of the propellers 1513, 1516 may be adjusted.During adjustment of the rotational phase alignment of the propellers,the sensor 1517 may continue to measure the generated sound to determinean alignment in which the generated sound is at its lowest.

In still another example, the pitch and/or other configuration of one ormore propeller blades of the lower propeller 1513 and/or the upperpropeller 1516 may be adjustable to alter the waveform of the inducedflow from the propeller as the propellers are rotated by the motor 1512.As the pitch of the propeller increases, the lift generated by thepropeller also increases for the same rotational speed. Likewise, thewaveform of the induced flow is altered. In some implementations, thesensor 1517 may measure the sound generated by the propulsion mechanismas the pitch of one or more propeller blades is altered to determinewhen a minimum sound level is reached.

The adjustment of the shaft (radially and/or rotationally), and/or thepitch of the propeller blades may be continuously or periodicallyperformed during operation of the aerial vehicle. Alternatively, certainareas or altitudes may be designated as reduced sound areas and theadjustment of the propulsion mechanism may only be made when the aerialvehicle is operating on those areas.

FIG. 16 illustrates another view of coaxially aligned and stackedpropellers, according to an implementation. In this example, thepropulsion mechanism 1600 includes a motor 1606 with a shaft 1605extending therefrom that is rotatable by the motor 1606. Threepropellers 1602-1, 1602-2, and 1602-3 are positioned along the shaft1605 in a coaxially aligned and stacked configuration. Similar to thediscussions above, the distance d₁ may be selected so that the soundfrom the high pressure pulse generated by rotation of the firstpropeller 1602-1 causes interference with the sound from the highpressure pulse generated by rotation of the second propeller 1602-2.Likewise, the distance d₂ may be selected so that the sound from thehigh pressure pulse generated by rotation of the second propeller 1602-2causes interference with the sound from the high pressure pulsegenerated by rotation of the third propeller 1602-3 and/or interfereswith a net effect resulting from the interference between the sound fromthe first propeller and the sound from the second propeller.

When the sound from the first propeller 1602-1 interferes with the soundfrom the second propeller 1602-2, the resulting combination is referredto herein as a net effect. If the interference is destructive, the neteffect may be a reduced amplitude and/or reduced frequency sound.Likewise, when the sound from the third propeller interferes with thenet effect sound, the two sounds combine and form a combined net effectsound.

In some implementations, the distance d₃ may also be selected so thatthe sound from the high pressure pulse generated by rotation of thethird propeller 1602-3 interferes with the sound from the high pressurepulse generated by the first propeller 1602-1.

As illustrated and discussed above, the propellers 1602-1, 1602-2, and1602-3 may have different sizes, diameters, chord lengths, cambers,pitches, thicknesses, etc. (generally characteristics) and generatedifferent lifting forces, have different operational efficiencies, andhave different sound profiles at the same RPM. For example, the firstpropeller 1602-1 may have a first diameter and a first pitch that isoptimized to generate a lifting force. The second propeller 1602-2 mayhave a second diameter and second pitch that is optimized formaneuverability, and the third propeller 1602-3 may have a thirddiameter and third pitch that is optimized for sound. While the exampleillustrated with respect to FIG. 16 shows the largest propeller beingclosest to the motor and the smallest propeller being furthest from themotor, in other configurations the different sizes of propellers may beat different positions along the shaft. For example, the largestpropeller may be furthest from the motor, at a mid-point betweenmultiple propellers, etc.

As discussed herein, the sounds expected to be generated by thepropellers, alone and/or in combination, may be measured and stored in amemory of the aerial vehicle controller for different RPMs of the motor.Likewise, based on the expected sound profiles of the propellers atdifferent RPMs, the distances d1, d2, and d3 may be selected to producea desired combined net effect when all three of the propellers arerotating and/or a desired net effect when two of the propellers arerotating.

In addition to or as an alternative to separating the propellers 1602 adefined distance so that generated sounds cause interference with oneanother, in some implementations, the different propellers may beindividually selectable such that a propeller adjustment controller 1608can individually engage and rotate one or more of the propellers 1602-1,1602-2, or 1602-3. For example, the propellers 1602-1, 1602-2, and1602-3 may be coaxially aligned, positioned along the shaft 1605 atdifferent distances and individually engaged by the propeller adjustmentcontroller 1608 such that the engaged propeller(s) rotates with arotation of the shaft. The propeller adjustment controller 1608 mayinclude a series of clutches 1608-1, 1608-2, and 1608-3 or gears thatcan be used to selectively engage one or more of the propellers 1602-1,1602-2, and 1602-3. In other implementations, the propeller adjustmentcontroller may include

In some implementations, the propeller adjustment controller 1608 mayreceive or determine an operational profile for the aerial vehicleand/or receive a commanded lifting force. Based on the differentcharacteristics maintained for the different propellers of thepropulsion mechanism 1600, the propeller adjustment controller mayselect and engage one or more propellers to generate the commandedlifting force that will optimize the propulsion mechanism according tothe determined operational profile. For example, if the operationprofile indicates that the propulsion mechanism is to be optimized forefficiency and/or lift, the propeller adjustment controller may engagethe first propeller 1602-1, which will generate the greatest amount oflift when the motor 1606 is rotating at a defined RPM.

In comparison, if the propeller adjustment controller determines thatthe propulsion mechanism is to be optimized for agility, the propelleradjustment controller may select and engage the second propeller 1602-2so that the second propeller 1602-2 is rotated by the motor at the RPM.As another example, if the propeller adjustment controller determinesthat the propulsion mechanism is to be optimized for sound, it mayengage the third propeller 1602-3 so that the third propeller 1602-3 isrotated by the motor at the RPM.

In some implementations, it may be determined that two or more of thepropellers are to be simultaneously engaged by the propeller adjustmentcontroller. For example, as discussed above, the first propeller and thesecond propeller may be coaxially and phase aligned and separated adistance d₁ so that the sound generated by the first propeller causesinterference with the sound generated by the second propeller to producea net effect that is a reduced sound. In such a configuration, thepropulsion mechanism may be optimized for lifting and sound at theselected RPM. For example, the lifting force generated by rotation ofboth the first propeller 1602-1 and the second propeller 1602-2 mayprovide sufficient lift at the RPM and the net effect resulting from thecombination of the sound from the first propeller and the sound from thesecond propeller may be less than a sound generated by the firstpropeller operating alone.

Propellers that are not engaged by the propeller adjustment controller1608 may be allowed to freely rotate about the shaft of the motor as theengaged propellers are rotated by the motor. Alternatively, thenon-engaged propellers may be secured in a fixed position with respectto the shaft so that the non-engaged propellers do not rotate when notengaged by the propeller adjustment controller.

In some implementations, the propeller adjustment controller maydetermine or receive a commanded lifting force to be produced by thepropulsion mechanism and determine, based at least in part on anengagement of the first propeller, the second propeller, and/or thethird propeller an RPM needed for the motor of the propulsion mechanismsuch that the engaged propellers will generate the commanded liftingforce when rotated.

FIG. 17 is a flow diagram illustrating an example propeller adjustmentprocess 1700, according to an implementation. The example process 1700of FIG. 17 and each of the other processes discussed herein may beimplemented in hardware, software, or a combination thereof. In thecontext of software, the described operations representcomputer-executable instructions stored on one or more computer-readablemedia that, when executed by one or more processors, perform the recitedoperations. Generally, computer-executable instructions includeroutines, programs, objects, components, data structures, and the likethat perform particular functions or implement particular abstract datatypes.

The computer-readable media may include non-transitory computer-readablestorage media, which may include hard drives, floppy diskettes, opticaldisks, CD-ROMs, DVDs, read-only memories (ROMs), random access memories(RAMs), EPROMs, EEPROMs, flash memory, magnetic or optical cards,solid-state memory devices, or other types of storage media suitable forstoring electronic instructions. In addition, in some implementations,the computer-readable media may include a transitory computer-readablesignal (in compressed or uncompressed form). Examples ofcomputer-readable signals, whether modulated using a carrier or not,include, but are not limited to, signals that a computer system hostingor running a computer program can be configured to access, includingsignals downloaded through the Internet or other networks. Finally, theorder in which the operations are described is not intended to beconstrued as a limitation, and any number of the described operationscan be combined in any order and/or in parallel to implement theroutine.

The example process 1700 begins by determining if the sound from theinduced flow of a propulsion mechanism is to be reduced, as in 1702. Insome implementations, it may be determined that sound from induced flowis to be reduced during any operation of the aerial vehicle. In otherimplementations, it may be determined that sound from the induced flowof a propulsion mechanism is only to be performed when the aerialvehicle is in designated areas or below designated altitudes.

If it is determined that the sound from the induced flow is not to bereduced, the distance between the propellers of the propulsionmechanism, the rotational phase alignment of the propellers, the pitchof one or more of the propeller blades, the rotational direction of thepropellers, the configuration of one or more of the propeller blades,and/or the engagement/disengagement of one or more of the propellers maybe adjusted so that the propulsion mechanism is optimized forefficiency, sound, or agility, as in 1704. For example, reducing soundusing the techniques discussed herein may increase the power consumptionrequired to rotate the propeller, thus reducing the efficiency of thepropulsion mechanism. If reduced sound is not needed, such as when theaerial vehicle is flying at a high altitude, the propulsion mechanismmay be adjusted to optimize for efficiency. In comparison, if it isdetermined that the aerial vehicle must maneuver in a small or confinedspace, it may be determined that the propeller configuration is to beoptimized for agility.

If it is determined that the sound resulting from the propulsionmechanism is to be reduced, the generated sound is measured by one ormore sensors positioned on the aerial vehicle, as in 1706. As discussedabove, the sensor may be positioned on a motor arm beneath the propellerof the propulsion mechanism, or at another location.

Based on the measured sound, a determination is made as to whether thesound exceeds a threshold, as in 1708. If it is determined that themeasured sound exceeds a threshold, at least one of the distance betweenthe propellers of the propulsion mechanism, the rotational phasealignment of the propellers of the propulsion mechanism, the pitch orother characteristic of one or more of the blades of the propellers ofthe propulsion mechanism and/or an engagement of one or more of thepropeller blades are adjusted to decrease or otherwise alter the soundgenerated by the propulsion mechanism, as in 1710. The process of makingone or more of the adjustments discussed with respect to block 1710 maybe continually performed until the measured sound is below thethreshold. Alternatively, adjustments may be periodically made and themeasured sound compared to a measured sound prior to the adjustment. Ifthe current measured sound is less than the prior measured sound,additional adjustments are made. If the current measured sound isgreater than the prior measured sound, the adjustment is removed. Thisprocess of adjusting one or more components of the propulsion mechanismmay continue until it is determined that the sound from the propulsionmechanism is no longer to be reduced (e.g., the aerial vehicle hasceased operation, or the aerial vehicle has navigated out of adesignated area). If it is determined that the threshold is notexceeded, the example process completes, as in 1712.

FIG. 18 is a flow diagram illustrating another example propelleradjustment process 1800 for altering a sound generated by a propulsionmechanism, according to an implementation. The example process 1800begins by determining an optimization factor for which the propulsionmechanism is to be optimized, as in 1802. For example, it may bedetermined whether the propulsion mechanism is to be optimized forefficiency, sound, or agility.

One or more environmental factors that may influence the generated soundfrom the propulsion mechanism may likewise be determined, as in 1804. Asdiscussed above, environmental factors may be intrinsic or extrinsic.Extrinsic data is data not directly relating to the aerial vehicle.Intrinsic data is data relating to the aerial vehicle itself. Forexample, extrinsic information or data may include, but is not limitedto, environmental conditions (e.g., temperature, pressure, humidity,wind speed, and wind direction), times of day or days of a week, monthor year when an aerial vehicle is operating, measures of cloud coverage,sunshine, surface conditions or textures (e.g., whether surfaces arewet, dry, covered with sand or snow or have any other texture) within agiven environment, a phase of the moon, ocean tides, the direction ofthe earth's magnetic field, a pollution level in the air, a particulatescount, or any other factors within the given environment. Intrinsicinformation or data may include, but is not limited to, operationalcharacteristics (e.g., dynamic attributes such as altitudes, courses,speeds, rates of climb or descent, turn rates, or accelerations; orphysical attributes such as dimensions of structures or frames, numbersof propellers or motors, operating speeds of such motors) or trackedpositions (e.g., latitudes and/or longitudes) of the aerial vehicles. Inaccordance with the present disclosure, the amount, the type and thevariety of information or data that may be captured and collectedregarding the physical or operational environments in which aerialvehicles are operating and correlated with information or data regardingmeasured sounds is theoretically unbounded.

The example process may also determine a lift to be generated by thepropulsion mechanism, as in 1806. For example, a commanded lift may bereceived or determined that is to be generated by the propulsionmechanism to aerially navigate the aerial vehicle along a flight path.The commanded lift may be determined and/or provided by one or morecomponents of the aerial vehicle control system.

Based on the determined optimization factor, desired lifting force to begenerated, and optionally the environmental factors, a configuration forthe propulsion mechanism is determined, as in 1808. Such configurationfor the propulsion mechanism may specify one or more of a propeller orpropellers to be engaged for operation, an RPM at which a motor is torotate the engaged propeller(s), and/or a configuration of the engagedpropellers (e.g., a pitch, alignment, chord length, camber, position,thickness, diameter, etc.), surface area, etc. Instructions are thensent that cause the propulsion mechanism to be configured accordinglyand the example process 1800 completes, as in 1810.

FIG. 19 is a view of an aerial vehicle, according to an implementation.As illustrated, the aerial vehicle may include a variety of differentpropulsion mechanisms, two or more of the propulsion mechanisms havingdifferent configurations. For example, propulsion mechanism 1902-1, asillustrated in the expanded view, may include a motor and a propellerwith two propeller blades. In some implementations, the propeller bladesof the propulsion mechanism 1902-1 may be fixed or adjustable, asdiscussed herein, such that one or more characteristics (e.g., pitch,angle of attack, camber, chord length, thickness, etc.) can be adjustedby a propeller adjustment controller.

Propulsion mechanism 1902-2 may include a motor with a series ofcoaxially aligned and stacked propulsion mechanisms, similar to theconfigurations discussed herein with respect to FIGS. 13-16. Likewise,the propeller blades of the coaxially aligned and stacked propellers ofpropulsion mechanism 1902-2 may be fixed or adjustable, as discussedherein, such that one or more characteristics (e.g., pitch, angle ofattack, camber, chord length, thickness, etc.) can be adjusted by apropeller adjustment controller.

Propulsion mechanism 1902-3 may include a motor with a propeller thatincludes a plurality of adjustable sections, similar to theconfigurations discussed herein with respect to FIGS. 11-12B.

Propulsion mechanism 1902-4 may include a motor with a series oftelescoping propeller blades, similar to the configurations discussedherein with respect to FIGS. 2-6. Likewise, the propeller blades of thetelescoping propellers may be fixed or adjustable, as discussed herein,such that one or more characteristics (e.g., pitch, angle of attack,camber, chord length, thickness, etc.) can be adjusted by a propelleradjustment controller.

The aerial vehicle 1900 may also include one or more sensors 1906configured to measure a sound generated by the aerial vehicle, asdiscussed herein. Likewise, the aerial vehicle may also include animaging element 1908 or other detection component that obtainsinformation regarding the environment in which the aerial vehicle isoperating. Such information, alone or in combination with otherenvironmental and/or flight plan information, may be used to selectconfigurations and/or optimization factors for the different propulsionmechanisms. For example, different propulsion mechanism may be selectedbased on the sound profile generated by each propulsion mechanism whengenerating a desired lift. For example, the first propulsion mechanism1902-1, to generate a desired lift may rotate at a first RPM andgenerate a first sound (PC-1 s). The second propulsion mechanism 1902-2,to generate the desired lift, may rotate at a second RPM that isdifferent than the first RPM and generate a second sound (PC-2 s) thatis different than the first sound (PC-1 s). The third propulsionmechanism 1902-3, to generate the desired lift, may rotate at a thirdRPM that is different than the first RPM and/or the second RPM andgenerate a third sound (PC-3 s) that is different than the first sound(PC-1 s) and/or the second sound (PC-2 s). The fourth propulsionmechanism 1902-4, to generate the desired lift, may rotate at a fourthRPM that is different than the first RPM, the second RPM, and/or thethird RPM and generate a fourth sound (PC-4 s) that is different thanthe first sound (PC-1 s), the second sound (PC-2 s), and/or the thirdsound (PC-3 s). In some implementations, the propulsion mechanismconfigurations may be selected so that the first sound (PC-1 s), thesecond sound (PC-2 s), the third sound (PC-3 s), and/or the fourth sound(PC-4 s) cause interference with one another thereby altering an overallsound, or combined net effect produced by the operation of the aerialvehicle. The interference may be destructive or constructive.Destructive interference results in the sound canceling out or producinga reduced combined net effect that has a lower amplitude and/orfrequency. Alternatively, the interference may be constructive and thesounds may combine to generate a combined net effect sound that is moreappealing to humans and/or other animals. For example, the combined neteffect sound may be a broadband sound, similar to white noise.

Configurations and/or selection of different propulsion mechanisms maybe predetermined for different lifting forces. For example, a table oflifting forces and propeller configurations that will generate soundsthat will cause interference with one another may be maintained by theaerial vehicle so that when a commanded lifting force is to be produced,the propeller configurations may be altered according to the table sothat the combined net effect sound produced by the aerial vehicle is aresult of interference between the sounds produced by the respectivepropulsion mechanisms.

In some implementations, the configurations of the propulsion mechanismsmay be optimized based on the environment in which the aerial vehicle isoperating. For example, if a human or other animal is detected by theimaging element 1908 to be within a defined distance of the aerialvehicle, the propulsion mechanisms may be optimized for sound. If theaerial vehicle is above a defined altitude or no humans or other animalsare detected, the aerial vehicle may be optimized for efficiency.

Based on the determined optimization factors, instructions are sent tothe respective propulsion mechanisms to configure the propulsionmechanisms accordingly. For example, as discussed above, expected soundprofiles, resultant lifting forces, and efficiency profiles may be knownfor each motor RPM and propeller(s) configuration. Such information maybe used to select a propulsion mechanism configuration for eachpropulsion mechanism so that a desired lifting force, sound profile,and/or optimization factors are provided by the different propulsionmechanisms.

In some implementations, the sensors 1906 may measure an overall soundgenerated by the aerial vehicle and send instructions to one or more ofthe propulsion mechanisms to make further adjustments to the propulsionmechanism to further alter and/or improve the overall sound generated bythe aerial vehicle. In some implementations, a sensor 1906 may bepositioned adjacent each propulsion mechanism to measure a soundgenerated by the propulsion mechanism such as sound PC-1 s, generated bypropulsion mechanism 1902-1, PC-2 s _(s) generated by propulsionmechanism 1902-2, PC-3 s _(s) generated by propulsion mechanism 1902-3,and PC-4 s _(s) generated by propulsion mechanism 1902-4.

Based on the measured sounds and the distance between each propulsionmechanism, alterations may be determined so that the different soundscause interference and produce a combined net effect that is a reducedtotal sound and/or a sound that is more appealing to humans and/or otheranimals (e.g., broadband noise or white noise). In some implementations,the aerial vehicle 1900 may utilize the imaging element 1908 and/orother detection component, such as a distance determining element, todetermine a position and distance of a human or other animal or objectwith respect to the aerial vehicle. Based on the position and distancebetween the aerial vehicle and the human, animal or other object, andthe known distance between the propulsion mechanisms, propulsionmechanism configurations may be determined and selected that willproduce sounds at a defined RPM so that when the sounds arrive at theposition of the human, animal or other object, each sound will interferewith the sounds generated by the other propulsion mechanisms of theaerial vehicle to produce a combined net effect sound at the position ofthe human, animal or other object that is less than the individual soundof a single propulsion mechanism and/or a sound that is more appealingto humans, animals, etc. For example, based on the speed of sound, theknown distances of the propulsion mechanisms, and the measured distanceto the human, animal or other object, propulsion mechanismconfigurations may be determined that will result in the differentsounds generated by the propulsion mechanisms being anti-sounds withrespect to one another that will combine and cause destructiveinterference at the location of the human, animal, or other object,thereby reducing or otherwise altering the total sound perceived by thehuman, animal, or other object at that location.

Referring to FIG. 20, illustrated is a block diagram of components ofone system 2000 for active sound control, in accordance with animplementation. The system 2000 of FIG. 20 includes an aerial vehiclecontrol system 2010 and a data processing system 2070 connected to oneanother over a network 2080. The aerial vehicle control system 2010includes a processor 2012, a memory 2014 and a transceiver 2016, as wellas a plurality of environmental or operational sensors 2020 and aplurality of sound control systems 2006. Each sound control system mayinclude a propeller adjustment controller 2006-2 and optionally a sensor2006-1.

The processor 2012 may be configured to perform any type or form ofcomputing function, including but not limited to the execution of one ormore machine learning algorithms or techniques. For example, theprocessor 2012 may control any aspects of the operation of the aerialvehicle and the one or more computer-based components thereon, includingbut not limited to the transceiver 2016, the environmental oroperational sensors 2020, and/or the sound control systems 2006. Theaerial vehicle may likewise include one or more control systems that maygenerate instructions for conducting operations thereof, e.g., foroperating one or more rotors, motors, rudders, ailerons, flaps or othercomponents provided thereon. Such control systems may be associated withone or more other computing devices or machines, and may communicatewith the data processing system 2070 or one or more other computerdevices over the network 2080, through the sending and receiving ofdigital data. The aerial vehicle control system 2010 further includesone or more memory or storage components 2014 for storing any type ofinformation or data, e.g., instructions for operating the aerialvehicle, expected propeller blade sounds at different configurationsand/or RPM, different expected propulsion mechanism sounds at differentconfigurations, or information or data captured by one or more of theenvironmental or operational sensors 2020 and/or the sound sensors2006-1.

The transceiver 2016 may be configured to enable the aerial vehicle tocommunicate through one or more wired or wireless means, e.g., wiredtechnologies such as Universal Serial Bus (or “USB”) or fiber opticcable, or standard wireless protocols, such as Bluetooth® or anyWireless Fidelity (or “Wi-Fi”) protocol, such as over the network 2080or directly.

The environmental or operational sensors 2020 may include any componentsor features for determining one or more attributes of an environment inwhich the aerial vehicle is operating, or may be expected to operate,including extrinsic information or data or intrinsic information ordata. As is shown in FIG. 20, the environmental or operational sensors2020 may include, but are not limited to, a Global Positioning System(“GPS”) receiver or sensor 2021, a compass 2022, a speedometer 2023, analtimeter 2024, a thermometer 2025, a barometer 2026, a hygrometer 2027,a gyroscope 2028, a microphone 2032, an imaging element 2034, and/or adistance determining element 2036. The GPS sensor 2021 may be anydevice, component, system or instrument adapted to receive signals(e.g., trilateration data or information) relating to a position of theaerial vehicle from one or more GPS satellites of a GPS network (notshown). The compass 2022 may be any device, component, system, orinstrument adapted to determine one or more directions with respect to aframe of reference that is fixed with respect to the surface of theEarth (e.g., a pole thereof). The speedometer 2023 may be any device,component, system, or instrument for determining a speed or velocity ofthe aerial vehicle and may include related components such as pitottubes, accelerometers, or other features for determining speeds,velocities, or accelerations.

The altimeter 2024 may be any device, component, system, or instrumentfor determining an altitude of the aerial vehicle, and may include anynumber of barometers, transmitters, receivers, range finders (e.g.,laser or radar) or other features for determining heights. Thethermometer 2025, the barometer 2026 and the hygrometer 2027 may be anydevices, components, systems, or instruments for determining local airtemperatures, atmospheric pressures, or humidities within a vicinity ofthe aerial vehicle. The gyroscope 2028 may be any mechanical orelectrical device, component, system, or instrument for determining anorientation, e.g., the orientation of the aerial vehicle. For example,the gyroscope 2028 may be a traditional mechanical gyroscope having atleast a pair of gimbals and a flywheel or rotor. Alternatively, thegyroscope 2028 may be an electrical component such as a dynamicallytuned gyroscope, a fiber optic gyroscope, a hemispherical resonatorgyroscope, a London moment gyroscope, a microelectromechanical sensorgyroscope, a ring laser gyroscope, or a vibrating structure gyroscope,or any other type or form of electrical component for determining anorientation of the aerial vehicle. The microphone 2032 may be any typeor form of transducer (e.g., a dynamic microphone, a condensermicrophone, a ribbon microphone, a crystal microphone) configured toconvert acoustic energy of any intensity and across any or allfrequencies into one or more electrical signals, and may include anynumber of diaphragms, magnets, coils, plates, or other like features fordetecting and recording such energy. The microphone 2032 may also beprovided as a discrete component, or in combination with one or moreother components, e.g., an imaging device, such as a digital camera.Furthermore, the microphone 2032 may be configured to detect and recordacoustic energy from any and all directions.

The imaging element 2034 may be any form of imaging element such as adigital camera, a video camera, a thermal imaging camera, or any otherform of imaging element that can obtain light based information aboutthe environment in which the aerial vehicle is operating. Likewise, thedistance determining element 2036 may be any form of distancedetermining element including, but not limited to, a time-of-flightsensor, an infrared sensor, a sound navigation and ranging (SONAR)sensor, a light detection and ranging (LIDAR) sensor, or the like.

Those of ordinary skill in the pertinent arts will recognize that theenvironmental or operational sensors 2020 may include any type or formof device or component for determining an environmental condition withina vicinity of the aerial vehicle in accordance with the presentdisclosure. For example, the environmental or operational sensors 2020may include one or more air monitoring sensors (e.g., oxygen, ozone,hydrogen, carbon monoxide or carbon dioxide sensors), infrared sensors,ozone monitors, pH sensors, magnetic anomaly detectors, metal detectors,radiation sensors (e.g., Geiger counters, neutron detectors, alphadetectors), altitude indicators, depth gauges, accelerometers or thelike, and are not limited to the sensors 2021, 2022, 2023, 2024, 2025,2026, 2027, 2028, 2032, 2034, and 2036 shown in FIG. 20.

The data processing system 2070 includes one or more physical computerservers 2072 having a plurality of data stores 2074 associatedtherewith, as well as one or more computer processors 2076 provided forany specific or general purpose. For example, the data processing system2070 of FIG. 20 may be independently provided for the exclusive purposeof receiving, analyzing or storing sounds, anti-sounds, tables, such asTable 1 discussed above, and/or other information or data received fromthe aerial vehicle or, alternatively, provided in connection with one ormore physical or virtual services configured to receive, analyze orstore such sounds, information or data, as well as one or more otherfunctions. The servers 2072 may be connected to or otherwise communicatewith the data stores 2074 and the processors 2076. The data stores 2074may store any type of information or data, including but not limited tosound information or data, and/or information or data regardingenvironmental conditions, operational characteristics, or positions, forany purpose. The servers 2072 and/or the computer processors 2076 mayalso connect to or otherwise communicate with the network 2080, asindicated by line 2078, through the sending and receiving of digitaldata. For example, the data processing system 2070 may include anyfacilities, stations or locations having the ability or capacity toreceive and store information or data, such as media files, in one ormore data stores, e.g., media files received from the aerial vehicle, orfrom one another, or from one or more other external computer systems(not shown) via the network 2080. In some implementations, the dataprocessing system 2070 may be provided in a physical location. In othersuch implementations, the data processing system 2070 may be provided inone or more alternate or virtual locations, e.g., in a “cloud”-basedenvironment. In still other implementations, the data processing system2070 may be provided onboard one or more aerial vehicles, including butnot limited to the aerial vehicle.

The network 2080 may be any wired network, wireless network, orcombination thereof, and may comprise the Internet in whole or in part.In addition, the network 2080 may be a personal area network, local areanetwork, wide area network, cable network, satellite network, cellulartelephone network, or combination thereof. The network 2080 may also bea publicly accessible network of linked networks, possibly operated byvarious distinct parties, such as the Internet. In some implementations,the network 2080 may be a private or semi-private network, such as acorporate or university intranet. The network 2080 may include one ormore wireless networks, such as a Global System for MobileCommunications (GSM) network, a Code Division Multiple Access (CDMA)network, a Long Term Evolution (LTE) network, or some other type ofwireless network. Protocols and components for communicating via theInternet or any of the other aforementioned types of communicationnetworks are well known to those skilled in the art of computercommunications and, thus, need not be described in more detail herein.

The computers, servers, devices and the like described herein have thenecessary electronics, software, memory, storage, databases, firmware,logic/state machines, microprocessors, communication links, displays orother visual or audio user interfaces, printing devices, and any otherinput/output interfaces to provide any of the functions or servicesdescribed herein and/or achieve the results described herein. Also,those of ordinary skill in the pertinent art will recognize that usersof such computers, servers, devices and the like may operate a keyboard,keypad, mouse, stylus, touch screen, or other device (not shown) ormethod to interact with the computers, servers, devices and the like, orto “select” an item, link, node, hub or any other aspect of the presentdisclosure.

The aerial vehicle or the data processing system 2070 may use anyweb-enabled or Internet applications or features, or any otherclient-server applications or features including E-mail or othermessaging techniques, to connect to the network 2080, or to communicatewith one another, such as through short or multimedia messaging service(SMS or MMS) text messages. For example, the aerial vehicle may beadapted to transmit information or data in the form of synchronous orasynchronous messages to the data processing system 2070 or to any othercomputer device in real time or in near-real time, or in one or moreoffline processes, via the network 2080. The protocols and componentsfor providing communication between such devices are well known to thoseskilled in the art of computer communications and need not be describedin more detail herein.

The data and/or computer executable instructions, programs, firmware,software and the like (also referred to herein as “computer executable”components) described herein may be stored on a non-transitorycomputer-readable medium that is within or accessible by computers orcomputer components such as the processor 2012 or the processor 2076, orany other computers or control systems utilized by the aerial vehicle orthe data processing system 2070, and having sequences of instructionswhich, when executed by a processor (e.g., a central processing unit, or“CPU”), cause the processor to perform all or a portion of thefunctions, services and/or methods described herein. Such computerexecutable instructions, programs, software, and the like may be loadedinto the memory of one or more computers using a drive mechanismassociated with the computer readable medium, such as a floppy drive,CD-ROM drive, DVD-ROM drive, network interface, or the like, or viaexternal connections.

Some implementations of the systems and methods of the presentdisclosure may also be provided as a computer-executable program productincluding a non-transitory machine-readable storage medium having storedthereon instructions (in compressed or uncompressed form) that may beused to program a computer (or other electronic device) to performprocesses or methods described herein. The machine-readable storagemedia of the present disclosure may include, but is not limited to, harddrives, floppy diskettes, optical disks, CD-ROMs, DVDs, ROMs, RAMs,erasable programmable ROMs (“EPROM”), electrically erasable programmableROMs (“EEPROM”), flash memory, magnetic or optical cards, solid-statememory devices, or other types of media/machine-readable medium that maybe suitable for storing electronic instructions. Further,implementations may also be provided as a computer executable programproduct that includes a transitory machine-readable signal (incompressed or uncompressed form). Examples of machine-readable signals,whether modulated using a carrier or not, may include, but are notlimited to, signals that a computer system or machine hosting or runninga computer program can be configured to access, or include signals thatmay be downloaded through the Internet or other networks.

Although the disclosure has been described herein using exemplarytechniques, components, and/or processes for implementing the systemsand methods of the present disclosure, it should be understood by thoseskilled in the art that other techniques, components, and/or processesor other combinations and sequences of the techniques, components,and/or processes described herein may be used or performed that achievethe same function(s) and/or result(s) described herein and which areincluded within the scope of the present disclosure.

For example, although some of the implementations disclosed hereinreference the use of unmanned aerial vehicles to deliver payloads fromwarehouses or other like facilities to customers, those of ordinaryskill in the pertinent arts will recognize that the systems and methodsdisclosed herein are not so limited, and may be utilized in connectionwith any type or form of aerial vehicle (e.g., manned or unmanned)having fixed or rotating wings for any intended industrial, commercial,recreational or other use.

It should be understood that, unless otherwise explicitly or implicitlyindicated herein, any of the features, characteristics, alternatives ormodifications described regarding a particular implementation herein mayalso be applied, used, or incorporated with any other implementationdescribed herein, and that the drawings and detailed description of thepresent disclosure are intended to cover all modifications, equivalentsand alternatives to the various implementations as defined by theappended claims. Also, the drawings herein are not drawn to scale.

Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey in apermissive manner that certain implementations could include, or havethe potential to include, but do not mandate or require, certainfeatures, elements and/or steps. In a similar manner, terms such as“include,” “including” and “includes” are generally intended to mean“including, but not limited to.” Thus, such conditional language is notgenerally intended to imply that features, elements and/or steps are inany way required for one or more implementations or that one or moreimplementations necessarily include logic for deciding, with or withoutuser input or prompting, whether these features, elements and/or stepsare included or are to be performed in any particular implementation.

Disjunctive language, such as the phrase “at least one of X, Y, or Z,”or “at least one of X, Y and Z,” unless specifically stated otherwise,is otherwise understood with the context as used in general to presentthat an item, term, etc., may be either X, Y, or Z, or any combinationthereof (e.g., X, Y, and/or Z). Thus, such disjunctive language is notgenerally intended to, and should not, imply that certainimplementations require at least one of X, at least one of Y, or atleast one of Z to each be present.

Unless otherwise explicitly stated, articles such as “a” or “an” shouldgenerally be interpreted to include one or more described items.Accordingly, phrases such as “a device configured to” are intended toinclude one or more recited devices. Such one or more recited devicescan also be collectively configured to carry out the stated recitations.For example, “a processor configured to carry out recitations A, B andC” can include a first processor configured to carry out recitation Aworking in conjunction with a second processor configured to carry outrecitations B and C.

Language of degree used herein, such as the terms “about,”“approximately,” “generally,” “nearly” or “substantially,” as usedherein, represent a value, amount, or characteristic close to the statedvalue, amount, or characteristic that still performs a desired functionor achieves a desired result. For example, the terms “about,”“approximately,” “generally,” “nearly” or “substantially” may refer toan amount that is within less than 10% of, within less than 5% of,within less than 1% of, within less than 0.1% of, and within less than0.01% of the stated amount.

Although the invention has been described and illustrated with respectto illustrative implementations thereof, the foregoing and various otheradditions and omissions may be made therein and thereto withoutdeparting from the spirit and scope of the present disclosure.

What is claimed is:
 1. An aerial vehicle apparatus, comprising: a frame; a first propulsion mechanism coupled to the frame at a first position, including: a first motor; and a first propeller coupled to the first motor and generating a first lifting force and a first sound when rotated by the first motor at a first revolutions per minute (“RPM”), the first propeller including: a first propeller blade having a first diameter and a first pitch; and a second propeller blade having the first diameter and the first pitch; a second propulsion mechanism coupled to the frame at a second position, including: a second motor; and a second propeller coupled to the second motor and generating the first lifting force and a second sound when rotated by the second motor at a second revolutions per minute (“RPM”), the first propeller including: a third propeller blade having a second diameter and a second pitch; and a fourth propeller blade having the second diameter and second pitch; and wherein the second sound is different than the first sound and the second sound causes interference with the first sound to produce a net effect that is different than the first sound and the second sound.
 2. The aerial vehicle apparatus of claim 1, wherein the first RPM is different than the second RPM.
 3. The aerial vehicle apparatus of claim 1, wherein the interference is destructive interference and the first sound cancels out at least a portion of the second sound such that the net effect has at least one of an amplitude or a frequency that is less than an amplitude or a frequency of the first sound.
 4. The aerial vehicle apparatus of claim 1, further comprising: a third propulsion mechanism at a third position on the frame of the aerial vehicle apparatus, the third propulsion mechanism configured to generate a third sound and the first lifting force; and wherein the third sound causes interference with at least one of the first sound, the second sound, or the net effect to produce a combined net effect.
 5. The aerial vehicle apparatus of claim 1, further comprising: a sensor configured to measure the net effect; and a controller configured to alter a configuration of the first propulsion mechanism based at least in part on the net effect measured by the sensor.
 6. An aerial vehicle apparatus, comprising: a frame; a first propulsion mechanism coupled to the frame at a first position, the first propulsion mechanism configured to generate a first lifting force and a first sound; a second propulsion mechanism coupled to the frame at a second position, the second propulsion mechanism configured to generate the first lifting force and a second sound; and wherein the second sound causes interference with the first sound to produce a net effect.
 7. The aerial vehicle apparatus of claim 6, further comprising: a first controller to alter a configuration of the first propulsion mechanism to cause the first propulsion mechanism to generate the first lifting force and a third sound.
 8. The aerial vehicle apparatus of claim 6, wherein the interference is destructive interference and an amplitude of the net effect is less than an amplitude of the first sound.
 9. The aerial vehicle apparatus of claim 6, wherein the interference is constructive interference and the net effect is a broadband noise.
 10. The aerial vehicle apparatus of claim 6, further comprising: a sensor configured to measure the net effect; a controller configured to alter a configuration of the first propulsion mechanism to cause the first propulsion mechanism to generate a third sound; and wherein the third sound causes interference with the second sound.
 11. The aerial vehicle apparatus of claim 6, further comprising: an imaging element coupled to the frame and configured to detect a presence of an object within a distance of the aerial vehicle apparatus; and a controller configured to determine a configuration of the first propulsion mechanism such that a third sound generated by the first propulsion mechanism will cause interference with the second sound to produce a net effect at approximately a location of the object.
 12. The aerial vehicle apparatus of claim 6, wherein: the first propulsion mechanism includes: a first motor; a first shaft coupled to and rotatable by the first motor; and a first propeller coupled to and rotatable by the first shaft, the first propeller including a first plurality of propeller blades, each of the first plurality of propeller blades having a first diameter and generating the first lifting force when rotating at a first revolutions per minute (“RPM”); and the second propulsion mechanism includes: a second motor; a second shaft coupled to and rotatable by the second motor; and a second propeller coupled to and rotatable by the second shaft, the second propeller including a second plurality of propeller blades, each of the second plurality of propeller blades having a second diameter and generating the first lifting force when rotating at a second RPM.
 13. The aerial vehicle apparatus of claim 6, wherein: the first propulsion mechanism includes: a first motor; and a plurality of propellers that may be extended or retracted with respect to the first motor; and the second propulsion mechanism includes: a second motor; a shaft coupled to and rotatable by the second motor; a first propeller positioned along the shaft; and a second propeller positioned along the shaft and separated a distance from the first propeller.
 14. The aerial vehicle apparatus of claim 13, wherein the first propeller and the second propeller are independently engaged by the second propulsion mechanism.
 15. The aerial vehicle apparatus of claim 13, further comprising: a third propulsion mechanism configured to generate the first lifting force and a third sound, wherein the third sound causes interference with at least one of the first sound, the second sound, or the net effect.
 16. A method for adjusting a plurality of propulsion mechanisms of an aerial vehicle, comprising: determining an optimization factor for the aerial vehicle; sending instructions to a first propulsion mechanism of the aerial vehicle to cause the first propulsion mechanism to at least: adjust to a first configuration determined based at least in part on the optimization factor; generate a first lifting force while in the first configuration; and produce a first sound; sending instructions to a second propulsion mechanism of the aerial vehicle to cause the second propulsion mechanism to at least: adjust to a second configuration determined based at least in part on the optimization factor; generate the first lifting force while in the second configuration; and produce a second sound; and wherein the first sound causes interference with the second sound to produce a net effect sound from an operation of the aerial vehicle.
 17. The method of claim 16, wherein the first configuration is different than the second configuration.
 18. The method of claim 16, wherein: the first propulsion mechanism operates at a first revolutions per minute (“RPM”) when in the first configuration; the second propulsion mechanism operates at a second RPM when in the second configuration; and the first RPM is different than the second RPM.
 19. The method of claim 16, further comprising: measuring the net effect sound produced by the operation of the aerial vehicle; and sending instructions to the first propulsion mechanism to alter the first configuration based at least in part on the measured net effect sound.
 20. The method of claim 16, wherein the optimization factor is an optimization for at least one of an efficiency, a sound, or an agility. 